The movie begins with the camera panning over New York City, past Coney Island and along a pier. Water rises from Brighton Beach and coalesces into the form of a huge being looking like a man-- the god Poseidon (Kevin McKidd). Poseidon strides through the water along the pier, glancing nonchalantly at a gawking fisherman, and steps onto the streets of New York, shrinking to human size and his garments changing to resemble normal contemporary attire. He arrives at the observation deck of the Empire State building and meets another man there, similarly attired-- his brother Zeus (Sean Bean), king of the Greek gods. Zeus asks Poseidon to look to the sky. Poseidon notes heavy thunderclouds, and Zeus points out there is no lightning-- his master bolt, which gives him control over lightning, has been stolen. Zeus gets directly into Poseidon's face and tells him that he is convinced that Poseidon's son is responsible for the theft. Poseidon insists that his son doesn't know who he is, and warns Zeus about crossing a line, and that if Zeus harms Poseidon's son, he will be in for the fight of his life, but Zeus does not back down. He tells Poseidon that unless the bolt is returned to him by midnight on June 21st, the summer solstice, there will be war.
We then see young teenager Percy Jackson (Logan Lerman) sitting calmly at the bottom of a swimming pool. On surfacing, he is told by his best friend Grover (Brandon T. Jackson) that he had been underwater nearly seven minutes. Hardly possible for most people, Percy thinks little of it. Being under water helps clear his mind and is one of the few places he can think.
Percy and Grover are at school at the Yancy Academy, and we see that Grover uses crutches. They walk through the halls, disgusted as several students fight openly in the halls before it is broken up by faculty. In class, there is a substitute teacher, Mrs. Dodds (Maria Olsen), writing a quote from Othello on the blackboard. She asks the class if anyone can explain the quote. Several students raise their hands, but Mrs. Dodds notices Percy glancing away and calls on him. He looks at the blackboard, blinking as the letters seem to twist and dance around confusingly in front of his eyes. Finally he says he doesn't know the answer.
Percy arrives home, kissing his mother, Sally (Catherine Keener), hello. She asks him about school and he is clearly very frustrated. Percy suffers from both dyslexia and ADHD, impairing his school performance. He thought the Yancy Academy was supposed to make things better. Sally tries to assure him that one day, everything will make sense, but he is very dubious.
At that moment the door opens and in walks Gabe Ugliano (Joe Pantoliano), Sally's husband and Percy's stepfather. Gabe is bald, paunchy, and dirty, with granny glasses attached to a chain around his neck. He sits at the table and asks where his beer is. Sally says it's in the fridge, but Gabe clearly expects her to bring it to him. Sally complies without a word of complaint, much to Percy's disgust. He insists that Gabe show some respect to Sally. Gabe gets up and leans against the wall close to Percy, and says that it's his house and Percy is the one who needs to show some respect.
Gabe retreats to his room and Percy asks Sally why she stays with him. Gabe Ugliano is a crass, crude pig of a man with foul armpit stench, who cannot hold a steady job because of his demeanor and smell. Sally tries to insist that Gabe is good to her and Percy in 'ways he doesn't understand.' Percy can only say that Sally is right-- he doesn't understand.
Percy is going with his school class to a museum to look at a gallery of ancient Greek and Roman exhibits. A voiceover from Poseidon tells Percy that everything as he knows it, is about to change. Percy glances around, and Poseidon is seen looking at him across the street, though Percy does not recognize him as he has never seen Poseidon before. A bus moves past Poseidon, in front of him, and he's gone.
At a gallery showing sculptures of the Greek gods, a teacher named Mr. Brunner (Pierce Brosnan) is lecturing on them. Mr. Brunner is in a motorized wheelchair, his legs covered in a blanket. Mr. Brunner explains how the gods often came down to Earth and had love affairs-- and sometimes children-- with mortals. He asks Percy if he can tell the class what these children were called. Percy correctly replies, 'demigods.' Mr. Brunner says that many of these demigods became great heroes, such as Hercules and Achilles. He then asks Percy to name another, giving him a hint: he has something in common with this hero.
Percy happens to glance up at a wall mural above Mr. Brunner's head. The Ancient Greek writing seems to dance and twist around before Percy's eyes, and to his surprise, he can read it: Perseus. Percy realizes that his own name is similar to Perseus.
As Mr. Brunner begins to explain the labors of Hercules and his victory over the Nemean lion, Mrs. Dodds quietly asks if she can speak to Percy alone, away from the other students. She opens a door into an adjacent, unfinished room, and enters behind Percy. But when he turns around, she is standing high up on a scaffolding.
In a harsh, grating voice, Mrs. Dodds demands, "Where is it?" Percy is completely confused, and then confounded as Mrs. Dodds changes into a hideous winged beast with long fangs that swoops down and demands that Percy give her the lightning bolt he stole. Percy is horrified and with no idea as to what is going on. The creature swoops again and seizes Percy, lifting him high up in the air and threatening to bite his heart out unless he returns the stolen lightning bolt.
Grover and Mr. Brunner burst into the room, The creature turns, recognizing Mr. Brunner, who demands that it release Percy or he'll tear the creature to pieces. The winged monster drops Percy and crashes through the window, flying off.
Percy is sick with disbelief at what happened-- and then even more so as Mr. Brunner turns to Grover and curses himself for not having realized that a "Fury" was concealed in their school. He asks Percy what the Fury wanted from him, and he shrugs and says that she said something about him stealing a lightning bolt. Mr. Brunner says in a very worried tone, "they found him," and Grover looks horrified, confusing Percy even further. Mr. Brunner tells Grover that Percy is no longer safe, and they should move him to "the camp." Percy confronts them on talking about him, right in front of him, without talking TO him. Mr. Brunner only hands Percy an object, telling him it is a powerful weapon and he should guard it well. Percy stares in amazement at what, to him, appears to be an ordinary writing pen. Mr. Brunner instructs Grover to bring Percy to Sally and not to take his eyes off of him. Grover nods and urges Percy to come with him. Neither Grover nor Mr. Brunner offer Percy any further answers, so for now he goes with Grover.
Hurrying down the street, Grover warns Percy to simply keep walking and not to look at anyone. Percy demands to know why Mr. Brunner wanted Grover to watch Percy, and Grover only says that he is Percy's protector. He insists he is quite capable of doing this despite apparently being on crutches.
At Percy's house, Gabe is playing poker with friends while Sally waits on them uncomplainingly. Percy comes in with Grover and urgently tells Sally they need to talk. Gabe crudely tells Percy to beat it, and Percy calls him a bald-headed freak. Gabe jumps up to hit Percy, but Grover slams a crutch down onto his foot and then hits him in the groin with it, which impresses Percy. Grover tells Sally that Percy has to leave immediately. Sally acquiesces and hurries out of the house with him.
Driving across a bridge, Sally is no more straight with Percy than Grover or Mr. Brunner had been. She only tells him that she's bringing them to a "camp for really special people." She says it's about Percy's father-- his true father.
As they drive on, Sally starts to tell Percy about how she met Percy's father... a man she never addresses by name. She says she was truly in love with him, and he loved her and Percy in turn. She admits that Percy's father left, but insists that he was forced to do it, and didn't abandon either of them.
As they drive past a field with cows, one horned head rises up, looking much larger than the other cows' heads. Grover suddenly shouts urgently for Sally to watch out. She gapes in horror as the corpse of a cow is suddenly thrown into the road right in front of them. Sally loses control of the car and it flips over.
The sound of heavy, ponderous footsteps begin to approach them. Percy stares as Grover removes his pants, revealing that his legs are those of a goat, complete with hooves. Grover uses them to smash through the car windshield so they can all get ouf of the car. The crutches, as he hurriedly says, are "just for show--" Grover can walk and run perfectly well, without them. The three of them flee from the approaching horror-- a huge bull-like humanoid. The monster picks up the car and hurls it at them.
They arrive at a stone arch surrounded by torches, which Grover says is their destination. As Percy stares up at the arch, Greek lettering dances around before his eyes to form recognizable words: "Camp Half Blood." He and Grover dash through the arch... but Sally is unable to pass through; some kind of barrier repels her. She urgently tells Percy that she cannot pass through the gate because she is "not like him." Percy refuses to leave without her but Sally begs him to do so. Just then, the huge minotaur grabs Sally from behind, and Percy watches in horror as the monster holds her aloft in one hand. She begs him to run, saying he's safe inside the gate, but Percy insists on facing the monster down. Grover shouts for him to take out the pen Mr. Brunner gave him, and click it. Percy does so and is shocked to see it transform into a Greek sword. The minotaur squeezes Sally and she screams briefly before disappearing in a flash of smoke and gold-colored dust.
Enraged, Percy charges at the minotaur, swinging the sword. The minotaur dodges and hurls a punch that blasts Percy into a tree. It charges at him on all fours, and he jumps away. One of the minotaur's horns lodges in the tree, and part of the horn breaks off when it tries to pull it loose. Percy grabs the broken-off horn as the minotaur charges again, and drives it into the monster's middle, killing it. Percy faints and collapses into Grover's arms.
He awakens lying in a cot with Grover watching over him. Grover is now clad in a leather vest with a dagger sheathed at his hip. He tells Percy that he is in the camp infirmary and has been unconscious for three days. He asks what Percy remembers. Percy thinks he awoke from a crazy dream, but then glances down and sees Grover's goat-legs and hooves. Grover says that he is a satyr. Percy breaks down in misery realizing everything was real, and his mother is gone. Grover tries to comfort him, saying he feels responsible as it's his job to protect Percy, although he is just a junior protector and doesn't have his horns yet.
Grover begins to take Percy around Camp Half Blood. People are seen in a mixture of modern and ancient Greek attire, and are training in combat with Greek weapons-- swords, shields, and bows. Grover finally begins to explain the truth about Percy, much to his continuing disbelief-- Percy is a demigod; one of hundreds throughout the world. Camp Half Blood is where demigods learn to harness their abilities, and while many go to lead "normal lives," many go on to become great leaders and heroes, though Percy cannot see himself as a hero. Grover then explains Percy's dyslexia and ADHD-- written letters and words seem to twist and dance around before his eyes because his brain is hardwired to read ancient Greek, not modern English; like back at the museum when he was able to read the Greek writing. And his ADHD is his divine battle reflexes. He was never able to be still, and this is what allowed him to survive-- and prevail, in his battle with the minotaur. As Grover says, no "loser" (as Percy thinks of himself) can defeat one.
Grover brings Percy to a field along a river where the students do most of their battle training. Percy stops and watches a beautiful young woman with long brunette hair battling several students at once-- and winning handily. She wields her sword with a grace and agility that Percy thinks he can only dream of. Percy asks Grover who she is, and he just laughs and warns him that the girl could tear him apart. But he says the girl's name is Annabeth (Alexandra Daddario), and she is the daughter of Athena, goddess of wisdom. Still holding her sword at the throat of her last opponent, Annabeth happens to look in their direction, her expression unreadable as she look at Percy, almost as if recognizing him.
Grover leads Percy to another field where he sees another amazing sight-- several centaurs engaged in a running exercise. But what's even more amazing is the lead centaur-- Mr. Brunner, or as he explains, here in this world, he is the legendary teacher, Chiron. He apologizes for hiding his true form, but he needed to keep an eye on Percy.
As they continue through the camp, Grover is called to by a group of daughters of Aphrodite, goddess of love. Chiron smirks as Grover goes to join them, suggesting to Percy that he knows where it will lead. Chiron brings Percy into a house which he says is Percy's quarters at the camp. The house is filled with nautical objects, and includes a heavy trident. Picking up the trident, looking at it, Percy realizes that some of the walls are carved with a symbol resembling the trident. Understanding dawns on him-- Percy is the son of Poseidon, god of the sea. Chiron says this has been kept from Percy for all these years for his own safety-- for a child to be sired by one of the "big three" Greek gods (Zeus, Poseidon and Hades) is exceptionally rare, and as the son of Poseidon, Percy is one of the most powerful of the demigods, which makes him a threat to the Olympian gods. Chiron then explains that Sally knew all of this, and the reason she married Ugliano was that his foul armpit stench hid and masked the smell of Percy's blood from anything that the gods could have sent to eliminate him. Percy is quiet and thoughtful as he realizes how much Sally sacrificed for him-- why she tolerated Gabe's treatment of her so gracefully.
Chiron then finally tells Percy about the reference to him as "the lightning thief--" Zeus' lightning bolt is the most powerful weapon ever created. Zeus' belief that Percy stole it centers aorund a very valid worry that it could pose a threat to Zeus' station as ruler of all the gods. Chiron warns Percy in a dire tone, that in ten days, if the bolt is not returned, the resulting war between Zeus and Poseidon would force all of Olympus to choose sides, and Earth would be torn asunder. Chiron plans to bring Percy to Olympus and make an appeal directly to Zeus as to Percy's innocence. As to why they can't go right now-- outside the gates are dangers; the Fury and the Minotaur being only the beginning. First, Percy needs to train so he will be able to handle these dangers.
Grover and Percy are heading to the training field; Percy suited up properly in leather and mail armor and feeling very awkward in it. Chiron orders all the students to fall in and gather around him. He introduces Percy to all the other students and says he will need a team. Stepping forth to volunteer to take him, is Luke (Jake Abel), son of Hermes and camp leader. Luke is a bit cocky and a bit of a jokester but takes to Percy right off. He gives Percy a helmet and welcomes him to his team-- the Blue soldiers. Chiron then orders all the students to prepare for game of Capture the Flag-- Ancient Greek style.
The two armies rush forth on command, swords and shields clashing. Luke tells Percy that he knows where the enemy flag is and to follow him. Ambushed by several Sons of Ares fighting for the red team, Luke and Percy fend them off, Percy amazed at having knocked out two of them. Luke urges Percy to hurry to the red flag while he holds off the rest of the Sons of Ares.
Percy hurries to a stream, where he removes his helmet and kneels to take a drink. But before he sips the water, he looks up and sees the red flag, completely unguarded, just across the stream. Grabbing his sword, he rushes in delight over to the banner.
But one red soldier is there to meet him-- Annabeth. The daughter of Athena quickly deals Percy several slash wounds and knocks him about the stream bank, seemingly toying with him. Chiron, Grover, Luke and a number of soldiers from both teams find their way there. Annabeth slashes Percy again and again, and kicks him down to the ground. The red soldiers cheer and gloat as she walks back to them.
Suddenly Percy hears his father's voice telling him to go to the water, and it will give him power. Slowly, painfully, he crawls to the stream. Everyone turns and looks as he dips his hand into the water. Curiosity turns to surprise and then shock as the water flows up his arm and shoulder, and over his whole body, healing all his wounds. Percy climbs to his feet, surging with new power and strength, and makes a beeline for Annabeth, easily swatting aside all Red soldiers that try to stop him. Quickly the tip of his sword is at her throat, and she looks at him in amazement. Regaining her focus, Annabeth bats Percy's sword aside and they fight once again. But this time Percy matches her, strike for strike, parry for parry. They grapple at close quarters and Percy wrests her sword from her grip, putting its blade to the back of her neck, and the point of his own sword to her throat as Grover and Chiron clap excitedly.
Annabeth surrenders, looking at Percy with a mixture of surprise at her defeat and admiration for the power he wields. He returns her sword and marches to the red flag. Nobody stands in his way as he plants his sword in the stream bank and lifts the red flag up high over his head in victory, the blue soldiers all cheering and applauding.
In the evening at dinner, Percy is approached by several nymphs inviting him to a party at their quarters. As he fills his cup, Annabeth comes up to fills hers, and they talk. Annabeth explains to Percy that her mother and his father have been long time enemies for many centuries. She says she has strong feelings for Percy, but hasn't decided if they're amicable or hostile yet.
The dinner feast is interrupted by the arrival of a massive, terrible winged demon appearing through a bonfire-- Hades. Hades calls Percy out and tells him that Sally is alive and well, but she is his prisoner, and he will release her to Percy only if he brings Hades the lightning bolt.
After Hades vanishes, Percy wants to travel to the underworld to negotiate Sally's release, thinking Hades will have no reason to hold her once Percy explains he didn't steal the ilghtning bolt and doesn't have it. But Chiron warns him that Hades doesn't work that way, and will kill both him and Sally. He insists that Percy stick to the original plan of appealing directly to Zeus first, and then they can formulate plans to rescue Sally.
Later that night, Grover finds Percy preparing to leave camp to set out for the Underworld, determined to rescue his mother. When Grover finds he cannot dissuade Percy, he insists on coming along, this being his job as Percy's protector. Annabeth also wants to come along. She's trained many years at the camp, but that's all she's done-- she's never embarked on an actual quest and hardly gotten to see the outside world. In addition, she's won a great many more battles than Percy, so her experience will come in handy. Percy is reluctant at first but then assents to their going with him.
The first puzzle is reaching the underworld... none of them knows how to get there. But Annabeth believes she knows who would.
The three of them visit Luke at his quarters, finding him playing video games. Luke's quarters are decked out with a lot of amenities from the modern world, including electronics, which he prefers over the "Renaissance Fair" decor of the camp. Annabeth knows that Luke's father, Hermes, as the messenger of the gods, has traveled to the underworld many times, and she asks if he knows anything about how to get there. Luke says he doesn't speak to his father and doesn't at all care for him ('we all have daddy issues,' he explains), but he says he broke into his father's house once and has some things that may help them. One is a pair of flying winged shoes, one of hundreds of pairs Hermes owns and uses to travel. Another is a map that will help locate three of the Pearls of Persephone. Luke explains that Persephone is more a prisoner of Hades than his wife, and she is miserable there. For comfort and companionship, she has many paramours and lovers. She gives them the pearls as a means of leaving the underworld unnoticed by Hades-- one needs only to crush a pearl underfoot and concentrate on where to go.
The map will help them find three of the pearls that are hidden in the United States. It shows one pearl located in a Garden Emporium owned by someone named Auntie Em, and located in Leeds Point, New Jersey. When the pearl is found, the map will show the location of the next one. When all three pearls are collected, the map will show where they can find a secret entrance to the underworld.
As a final gift, Luke asks Percy to take his favorite shield, saying it will be of help to him.
Percy, Grover and Annabeth catch a bus and make their way to Auntie Em's garden Emporium. They find it seemingly unoccupied and nearly delapidated; what appears to be an icebox with free soft drinks only contains a nest of rats. There are a lot of stone statues around. Annabeth notices a stone fountain with a number of Greek gold drachmas, meaning they're on the right track. She gives them to Percy. The three decide to split up and search the whole Emporium, hoping to find the pearl.
Annabeth walks past more statues, eerily carved as if cowering in terror from whatever they are pointed to face. Suddenly a strange, middle-aged woman rushes up out of nowhere, hysterically begging for her help. Barely coherent, she only manages to get out that she and her husband stopped for directions. She grabs Annabeth's forearm, hysterically begging for Annabeth to come and help her.
Grover finds his way to a shed where one of the statues is of a satyr, which strongly resembles his uncle Ferdinand. In fact, it's a near perfect stone replica of him, right down to the mole on his forehead. Grover muses, deciding it can't be his actual uncle, because he was killed by...
Grover freezes in horror. His uncle was killed when he was turned to stone by Medusa. Auntie *EM's* Emporium... M for Medusa. Frantically he rushes to find Annabeth and Percy. Percy hears Grover's frantic yells that they are all in trouble. He grabs his pen and activates it as his sword and rushes to rendezvous with him. Meanwhile, Annabeth is still being pulled by her wrist, by the hysterical woman, who is screaming that they have to leave before "she" finds them... a woman who turned her husband to stone.
The scene switches back and forth a few times between Percy and Grover, running through the Emporium grounds trying to find each other... and find each other they do, literally running smack into each other. Grover tells Percy that they're in Medusa's lair. They still need to find Annabeth.
Annabeth is still being pulled along by the hysterical woman, who realizes she is lost on the Emporium grounds and is terrified they'll never get out alive. Suddenly they stop short, Annabeth saying not to move. Standing right in front of them, a turban-like cloth wrap over her head and dark shades over her eyes, is Medusa (Uma Thurman).
Medusa speaks slowly and seductively, telling how she creates her 'statues' which serve as her only company in such a 'lonely' place. Suddenly she addresses Annabeth as 'daughter of Athena,' showing Medusa recognizes her for who she is. Medusa explains that she once had the same beautiful brown hair as Annabeth. Toying with a few locks of Annabeth's hair, Medusa explains that she was desired and courted by many suitors, which made Athena jealous, and led her to curse Medusa.
Medusa steps back and removes her headpiece, revealing the snakes that serve as her hair, as Annabeth urges the hysterical woman not to look. Both of them snap their eyes shut as Medusa's tone turns stern, saying that eyes are the windows to the soul, and she hopes they find hers attractive. She removes her dark shades, revealing her terrible blue eyes with the power to turn people to stone. Her tone turning seductive again, she gently whispers for them to 'sneak a peek' at her eyes.
The lure proves too much for the hysterical woman, who looks at Medusa's eyes and promptly turns to stone; her now-stone hand still locked around Annabeth's wrist.
Percy and Grover arrive, behind Medusa, and she isn't yet aware of their presence. Percy knows that they can look at her reflection safely, and takes out his iPhone. Grover says he'll get Annabeth away.
Medusa cockily puts her sunglasses on the hysterical woman's left wrist and gets very close to Annabeth, taunting her that she will eventually open her eyes. Medusa gets close enough that her hair-snakes flick through Annabeth's hair and across her cheeks. Annabeth trembles in fear, desperately fighting to keep her eyes tightly shut.
Hearing Medusa speak, Percy calls out, trying to give Annabeth resolve to keep her eyes closed. Medusa hears Percy's voice and whirls around, realizing that the new arrival is another demigod. She heads toward the sound of where Percy's voice came from. Percy runs, leading Medusa away from Annabeth, using the reflection in his iPhone to keep track of Medusa. As Percy pauses behind a statue, Medusa stops, recognizing Percy by the smell of his blood as the son of Poseidon. She remarks that she used to date Poseidon before pushing one statue down, causing it to topple a line of statues like dominoes; the last one landing on Percy.
Annabeth struggles futilely to free her wrist from the now-stone woman's grasp, still not daring to open her eyes. Grover comes up and uses a crutch to smash the woman's arm off, freeing Annabeth. The two rush to rendezvous with Percy.
Trying to crawl out from under the statue, Percy reaches for his sword, but Medusa kicks it away and lifts Percy by the scruff of his neck. Percy jams his eyes shut as Medusa holds him close to her face and tells him that she hears he has the stolen lightning bolt. She leans her head in close and tells Percy that her 'hungry babies' can open Percy's eyes for him if he doesn't do it himself. She sweetly says that he can stay with her always; all he has to do is look.
Medusa's soft and seductive whisper almost has Percy about to open his eyes when Grover and Annabeth arrive on the scene, driving the pickup truck owned by the hysterical woman and her husband (they don't need it anymore). They smash through several statues, knocking Medusa down.
Medusa hisses angrily, looking about for Percy. She finds his iPhone and peers curiously at it. Distracted, she doesn't hear Percy coming up behind her. She spots his reflection in the iPhone too late-- Percy beheads her with a swift stroke of his sword.
Grover and Annabeth exit the truck, tapping fists in celebration of vanquishing Medusa. Though Grover is repulsed at the idea, Annabeth says they need to take Medusa's severed head with them. If they open her eyes, their power to turn living beings to stone still works. Percy asks Grover for his jacket so they can wrap up the head. Grover gives Percy his hoodie instead.
After giving the head to Grover, Percy happens to look again at Medusa's headless body and realizes that she is wearing a bracelet with the pearl set into it. He pries it free and the three of them drive off in the pickup truck.
As they head down the road, Annabeth wonders why Luke didn't warn them about Medusa (why indeed....) Grover asks Percy to open up the map so it will show them where the next pearl is. The map reveals the location as a replica of the Greek Parthenon... in Nashville, Tennessee (much to Grover's disgust; he hates country music).
It is late at night and they are still on the road. Percy and Annabeth are fast asleep, and Grover starts to nod off at the wheel. The blare of an eighteen-wheeler's horn jolts them all awake and Grover barely swerves away. The three of them, shaken, decide to stop for the night. They make their way to a roadside motor inn and get a room.
Just before sunrise, Percy is in the swimming pool, sitting on the pool floor as he loves to do. An image of his mother, and Hades holding her prisoner, flashes through his mind. He looks up and notices Annabeth standing at the poolside, watching him. He surfaces and she sits down, her feet in the water. Percy notices the bruises on Annabeth's wrist from the woman who was turned to stone by Medusa. Gently taking her arm, he heals the bruises for her through his connection to the water. He climbs up and sits beside her at the poolside and asks why Poseidon and Athena are enemies. She explains it started when they vied for patronage of Athens and the people of the city chose Athena. Percy asks what Athena is like, but Annabeth doesn't know-- like Percy and Luke, she's never met her divine parent. Percy is surprised, wondering if any demigod has ever met their divine parent. Annabeth explains that this is forbidden by Zeus himself... he decreed that all gods were prohibited from having any physical contact with their half-mortal children. Both agree that the law is ridiculous, though Annabeth tells Percy that she believes she hears her mother speaking to her in her mind in times of trouble, giving her advice. Percy realizes that's the same as the voice he hears in his head, and Annabeth says that's Poseidon talking to him.
An urgent shout from Grover recalls them to their room. A news article on TV has listed Percy as a missing person... and a suspect in the disappearance of Sally. To Percy's revulsion, Gabe Ugliano is interviewed in the news segment, spouting lies about Percy having been on drugs and alcohol; and five nights ago, Percy tried to kill him and threw Sally on the ground, before Percy's 'cripple friend' attacked Gabe from behind (Grover gapes in astonishment at the preposterous story), and Percy kidnapped Sally and took her away. Percy shuts off the TV in disgust, figuring he is now a fugitive.
Grover goes to the bathroom to pee and groans as he sees that Percy placed Medusa's head there. He holds it up and admonishes Percy for putting it there. A maid working at the motor inn passes by the window and sees, and screams as she rushes away. Grover curses himself for having left the curtains open. Annabeth realizes they have to leave right away.
They arrive in Nashville at daytime. making their way to Centennial Park where the replica of the Parthenon is located. Inside, they stand before a huge statue of a Greek warrior woman. Percy is able to read the Ancient Greek on the nameplate and sees it is a statue of Annabeth's mother, Athena. Annabeth gazes up at the statue, wondering if her mother really looks the way she is depicted, and she smiles when Percy assures her that they'll find out. Grover looks up at a golden headdress set on the statue's head and notes that the pearl is set into the centerpiece of it.
This presents a problem-- how to get up 30 feet in the air, especially while the place is filled with tourists. Percy has an idea to the solution. The three of them hide in bathroom stalls, standing on them so their legs and feet aren't seen, and wait for the place to close for the night. An hour after the park closes they come out, with the plan being for Percy to use the flying shoes to get up to the head of the statue. But although the park is closed, the Parthenon isn't quite empty... night custodians are there, cleaning the place. Annabeth loads a hand crossbow and darts between pillars, stealthily and quickly taking the custodians out with drugged darts. Grover drags the sleeping custodians to one side of the Parthenon as Annabeth sets up her wireless laptop and makes a conference call to Luke, to get instructions on activating the flying shoes. Luke quickly explains that Percy needs to get a running start and build up speed, and that it will take some practice. But Percy proves more adept than this, and although he nearly loses his grip on the statue, he is able to climb back up the pry the pearl out from the headdress. Guided by the shoes to an easy landing on the ground, they all tap fists and Annabeth hugs Percy, telling everyone to gather up their things.
But they're not out of the woods yet... the custodians have recovered and form a line in front of the exit. Grover tries to bluff them by acting like he's a Park Recreational Services manager. But it quickly becomes apparent that these custodians are not ordinary people. They address Percy by name and demand the return of the lightning bolt. Percy sighs in exasperation, but his protest that he doesn't have it falls on deaf ears. One custodian coughs a puff of fire, and then all five of them merge into a giant monster... the five-headed hydra. Percy, Annabeth and Grover rush behind pillars as the middle head spews a cone of roaring flames. Percy's jacket is ignited, and when he shakes his arm to quell the flames, he loses his grip on the pearl, which flies across the Parthenon, resting on top of a flood drain grille. Activating his sword and shield, Percy takes to the air, and despite Annabeth's urgent warnings, he begins slicing off the heads of the hydra.
The hydra collapses as the last head is severed, and Percy and Grover start to high-five. But Annabeth admonishes them that Percy only made the problem worse. She's the only one of the three that remembers that when one head of the hydra is cut off, two more grow back in its place.
A terrible roar and the ground shaking prove the point of Annabeth's admonishment as the hydra rises again... now with ten heads; two of which spout flame. Percy tells Annabeth to distract it while he retrieves the pearl. Annabeth draws her bow, loosing several arrows to harass the hydra. But although one head is hit squarely in the eye, the hydra still turns as Percy dashes for the pearl, and the two central heads spew gouts of fire. Percy dives away, using his shield to protect himself, but the shield is thrown from his grasp several yards away. As the hydra closes in, Percy notices emergency fire hoses. Reaching out and concetrating, Percy summons the water from its holding tanks to form a wall between himself and the hydra. The wall of water also acts as a shield against the hydra's flaming breath, and allows Percy to retrieve the pearl. He dashes for the door, Grover and Annabeth right behind him... but they realize the hydra will reach them before they can get the door open. Grover gets an idea and rushes back toward the hydra, grabbing Percy's backpack. He grabs the head of Medusa, and snapping his eyes shut, points the face at the hydra and removes the shades from Medusa's eyes. Quickly the eyes begin to flash and the snake heads begin to thrash about. The flames stop short of the head and the hydra turns to stone.
The three adventurers make their way to an all night diner to eat. During the meal, they see a special news bulletin on the TV where scientsts are at a loss to understand a single storm cloud that has grown so massive as to spread over much of Europe and Asia. The cloud is expanding westward toward the United States, and much of the world's coastlines are experiencing gale-force winds and massive surf waves. Annabeth realizes the gods are angry, and they need to get the last pearl quickly. They examine the map and find that it is in Las Vegas, Nevada, at the Lotus Hotel and Casino.
As they approach the casino, they need to fight to remind themselves that they're only there for the pearl, not for any form of entertainment. Right away a casino employee tries to make them accept a casino fun book, and they have to assert themselves that they aren't checking in. Grover figures that since the cocktail waitresses are all wearing green dresses, perhaps one of them has the pearl.
Several waitresses quickly surround them, holding trays filled with cookies that they call Lotus Flowers-- the casino's signature dish. Tentatively, the three of them each try a sample. They find the cookies exquisitely delicious... not even noticing the psychedelic effect the 'lotus flowers' have on them. They start to laugh and giggle in growing excitement as they continue to look around them. In half a minute they've forgotten what they're there for, except to have fun and enjoy themselves. The decision to stay-- perhaps as permanent fixtures of the casino-- is a no-brainer.
Percy, Annabeth and Grover all start to partake in the casino's festivities-- gambling, dancing, partying... and of course more of the delicious lotus flowers. But finally, just as Percy is about to eat one, he hears his father's voice admonishing him not to. The flowers dull their senses and keep them prisoner in the casino. Crinkling his brow, he excuses himself from Annabeth to walk around, and leaves the lotus flower uneaten on the bar. He begins to walk through a video arcade, declining all the waitresses who swarm around with their flower trays. Poseidon's voice guides him, telling him to focus. He passes a young man playing a pinball machine themed after the movie, The French Connection. The young man asks if Percy's seen it, and Percy is stunned when the young man doesn't understand him when he says he's seen it on DVD. Quickly he realizes that the young man thinks that the year is still 1971; the year the movie was first released. Percy starts to snap out of it, guided by Poseidon's voice. He realizes the cocktail waitresses are redoubling their efforts to serve him more lotus flowers and starts to understand the entrapment effect of them. Then he walks past a roulette table and sees that the roulette ball is the pearl he came for. This jolts him completely back to his senses. As he walks away from another waitress trying to make him have another lotus flower, a bellhop turns and speaks into a headphone: 'Percy Jackson's awake.'
Percy hurries back to Annabeth, finding her dancing with several young women. He grabs her and herds her to where Grover is being tended to by a group of gorgeous young women. Pulling a satyr away from beautiful women is hard enough when Grover is sober, but Percy manages to do it. Raising his voice to an urgent pitch, he finally gets through to them that the lotus flowers are putting them in a trance and making them want to stay and party. The sight of security guards converging on them helps break the trance on Annabeth and Grover. Together with Percy they must now fight their way through the guards back to the roulette table where Percy grabs the pearl. Rushing to a car on display as a prize that can be won, they use it to escape from the casino.
Racing down the street until they feel a safe distance away, they recollect their thoughts. Annabeth realizes the casino is the lair of the Lotus Eaters-- and the 'casino' is where they have trapped people since ancient times. Even more dire is Grover passing a large display LCD calendar sign... the date is no longer June 15th, but June 20th... they'd spent five days and nights in the Lotus Casino's trap. The deadline being only a day away, they consult the map, finding the entrance to Hades is in Hollywood. Grover nods grimly, saying he can get them there in four hours.
As they pull up before the famous Hollywood hillside sign, the radio gives a news report that the storm clouds have covered most of North America. Several states are ordering evacuations as the weather grows more severe. They run along the sign's letters, pausing as Percy notes that some of the graffiti appears to be written in Ancient Greek. Quickly he reads it: 'Woe to all depraved souls.'Quickly a patch of ground beside the letter opens up, revealing an entryway deep underground... which closes up behind them as they walk in.
They make their way down a subterranean tunnel with torches and lots of skulls in the earthen walls. Presently they come to a mysterious man in a long hooded robe, standing in a canoe float in a dark river beside the platform. Approaching him, they see he is the ferryman who brings souls to Hades' kingdom. The ferryman refuses to bring them to Hades because they are still living. He tells them to come back when they are properly dead. Grover tries to bribe the ferryman with several bills of American currency. But, looking at them curiously, the ferryman burns them to ash in his hand, letting the ashes fall through his fingers.
Percy realizes Grover was on the right track but used the wrong kind of currency. He gives the ferryman the gold drachmas taken from the fountain in Medusa's lair. This, the ferryman accepts, and takes them across the legendary River Styx, which is filled with centuries of broken human dreams and sorrows; wishes and hopes that never came true.
Percy, Grover and Annabeth walk into the entrance to Hades' palace. They are promptly greeted by three hellhounds that guard their master's domain. THe hounds are called off by Persephone (Rosario Dawson) who brings them to Hades. The three adventurers are surprised to see that Hades has taken on human form as well (played by Steve Coogan). Hades reveals he is seeking Zeus' lightning bolt because it would allow him to overthrow his brothers and escape from the underworld, where he was exiled by Zeus. If Zeus and Poseidon destroyed each other in a war, he would be able to take over Olympus.
Percy tries to explain that he doesn't have the lightning bolt, but Hades doesn't believe him. He picks up an orb and shatters it on the ground, revealing that this was where he had been keeping Sally imprisoned. Percy rushes forth to hug Sally, grateful that she is alive and well.
But slowly everyone starts to become aware of Hades staring intently at Luke's shield, which Percy had dropped to the ground in order to hug his mother. The handgrip of the shield has opened up after being dropped, to reveal a secret compartment inside it. Inside this compartment is the missing lightning bolt.
Percy, Grover and Annabeth realize that Luke was behind the theft of the lightning bolt all along, but none of that matters to Hades. He only cares that he has what he wanted. Picking up the bolt, he breaks his word to Percy and orders Persephone to feed Percy, Grover, Annabeth and Sally to 'the souls.'
Persephone gestures and a grille over what looks like a fireplace, opens up... but behind this grille is no mere fireplace, but a furnace of damned, burning souls that start to writhe outward, smelling the living souls they are about to receive. Persephone then calls the hellhounds to herd the three adventurers toward the flames. Hades gloats with wicked glee at how he will rule the gods. Persephone grins wickedly and grabs her husband for an amorous smooch.
Or not so amorous, as while Hades is distracted, Persephone snatches the lightning bolt out of his hands and zaps him with it, knocking him unconscious. Quickly she calls off the hellhounds and closes the furnace gate. Kneeling over Hades, Persephone gloats at how he will remember nothing of all these recent events when he wakes up. Although grateful, Percy is curious as to why Persephone is helping them. She explains that Hades treats her like dirt, and all she has to look forward to while in his domain, is her alotted time back on Olympus. A war of the gods would destroy all that, and leave her alone with only Hades for company-- the worst kind of company she could dread havinag to keep. She gives Percy the lightning bolt and tells him to take it, and Sally, away.
But as Percy takes out the pearls, it quickly becomes evident that there is a problem. There are three pearls, and three members of Percy's party (himself, Grover and Annabeth)... but Sally makes a fourth person, and each pearl only grants egress to one. This means one of them has to stay behind in the underworld. There is a brief argument between Percy and Annabeth, both of whom feel they should be the one to stay... until Grover says that as Percy's protector, it's his duty and job to take on the burden. Persephone is delighted at this and promises to "take very good care" of Grover.
Percy, Annabeth and Sally use the pearls to take them to Olympus, but Percy is confused when they arrive at the observation deck of the Empire State Building. Annabeth points out the terrible storm clouds above-- Zeus and Poseidon preparing for battle. Sally assures Percy that they are in the right place and shows him an entrance to a service closet that contains the secret entrance to Olympus.
But Percy is not quite home free yet. There's ten more minutes until the midnight deadline, and Luke has arrived, wearing another pair of his father's flying shoes, to make sure Percy misses that deadline. Questioned by Percy, Luke reveals that when Percy, Grover and Annabeth came to see him about traveling to the underworld, he saw it as the perfect opportunity to dupe Percy into the very role Hermes normally performs... messenger of the gods. Luke hid the lightning bolt in the shield and gave the shield to Percy, so that Percy could unwittingly deliver the bolt to Hades. Reminding Percy that he bears as much animosity toward his divine parent as nearly all the demigods have for theirs, Luke wants to see them go to war and destroy themselves, believing that the demigods could then take over and rule the world as they see fit.
Swooping at Percy, Luke knocks him to the ground and seizes the lightning bolt. Drawing a dagger, Annabeth engages him and fends him off, although she cannot defeat Luke while he has the lightning bolt and the flying shoes. Luke takes off into the skies. Percy reaches into his backpack and takes out the flying shoes Luke had given him, and takes off in pursuit.
Luke is about to cast lightning at a passing helicopter when Percy dives at him. They wrestle in mid-air until Luke breaks free and tries to blast Percy with lightning. There is a brief cat-and-mouse game through a skyscraper's interior until Percy catches Luke by surprise and wrests the lightning bolt from him. Now it is Luke pursuing Percy, trying to recover it.
Percy is almost back at the Empire State Building when Luke hurls a knife that slices the wings off of Percy's flying shoes. No longer able to control his flight, Percy tumbles to a hard landing on a rooftop. Luke picks up the lightning bolt, and questions Percy's heritage as son of Poseidon. Percy sees several water towers atop nearby buildings and concentrates, breaking the tanks open and gathering the water to deluge Luke. Gathering some of the remaining water and shaping it into a trident, Percy says that he must be the son of Poseidon after all. Hurling the trident, he catches Luke across the throat between two of the prongs, taking Luke clear out of his flying shoes and casting him into the river.
Donning Luke's shoes, Percy arrives back at the Empire State building with the lightning bolt. Sally and Annabeth flip several switches in a control box in the service closet, which acrivates the hidden secret elevator that takes them all up, far past the roof of the building, into the heavens before the gates of Olympus. Sally, as a mortal, is unable to venture forth onto the divine ground. Annabeth and Percy rush to the hall of the gods.
Inside the hall, the deities of the Greek Pantheon are engaged in heated argument until Zeus demands silence and crosses to a time-dial in the center of the great hall. Poseidon and Athena, despite their enmity, both make a final appeal to Zeus to avoid war. But as the time-dial signals the arrival of midnight and the passing of the deadline, Zeus is about to pronounce judgement of war. Just then, Percy and Annabeth rush into the hall bearing the lightning bolt. Zeus demands its return, and Percy does so. The bolt grows to its true size in Zeus' grasp. He says that Percy is wise to betray his father. Percy retorts that he was never working with or for Poseidon's benefit, and he reveals Luke as the true lightning thief (to the great surprise of Hermes (Dylan Neal)), explaining that Luke resented all the gods for not caring about their children, and he wanted them to destroy each other so the demigods could rule Olympus. The gods all look around at each other, seeing how they had been played and pitted against one another. Zeus accepts Percy's explanation and declares peace. Athena (Melina Kanakaredes) smiles at Annabeth and tells her she's very proud of her.
Percy mentions that he and Annabeth escaped the Underworld only because Grover stayed behind. Zeus smiles cynically as he realizes that Percy wants him to return Grover to the world of the living. However, he agrees to the request. Zeus declares the convening of the gods to be adjourned. Poseidon makes a plea to his brother that he be allowed to speak to Percy, and Zeus consents-- but just this once.
Percy is naturally resentful that Poseidon was never around, and that he never got to even meet him. Poseidon acknowledges that Percy was only seven months when he left him and Sally. He says that being with him and his mother, Sally, made Poseidon start to forget his duties and become more human, which Zeus didn't approve of. Percy is surprised on hearing that Poseidon's siring him was what led Zeus to pass the divine rule prohibiting the gods from having any contact with their children. Poseidon manages to come to terms with Percy, saying he never wanted to leave him or Sally, and was in fact always with him in heart and spirit; Percy acknowledging he heard Poseidon's voice when he spoke to Percy. Poseidon promises that while he might not get to see Percy again, he will always be there with and for him-- in his heart, in his thoughts, and in his dreams. Percy forgives his father and shakes hands with him.
Sally brings Percy back to Camp Half Blood, where he can fulfill his destiny as a demigod. Although she will miss him, she says it's where he belongs. She also says, to Percy's great relief, that she is finally kicking Ugliano out of the house, now that he has served his purpose and she doesn't need him anymore.
Percy is welcomed by everyone back at the camp, and Grover shows him that he's been promoted to senior protector, and has finally gotten his Satyr horns. Chiron starts to admonish Percy for disobeying his orders and leaving camp without permission, but then says that this is why Percy is now his favorite student-- many times he simply has to follow his own instincts. But hero or not, Percy is, to Chiron, still one of his students, and He sends Percy to suit up for more training.
As Grover and Percy walk through the training area, Grover amuses Percy with stories of Grover's time in the underworld as Persephone's paramour. They find Annabeth in the same manner in which Percy first set eyes on her-- she is taking on several other students in swordplay at the same time, holding her own and more. Grover pats Percy's shoulder and tells him that he can handle this on his own now. After defeating the last of her opponents, Annabeth calls for the next one, and Percy steps up to volunteer. Annabeth puts a hand on his neck, welcoming him home and leaning in as if to kiss him. Suddenly with a mischevious look, she surprises Percy by swiping his sword out of its scabbard and pointing her own at him, telling him that he must never be distracted by an opponent. Percy grins and motions for his sword back. She returns it and they square off. The camera slowly pans back as Percy and Annabeth begin their battle, and the credits start to roll.
Midway through the credits is an extra scene showing Sally telling Gabe to take all his things with him. He goes to the kitchen in disgust for a beer and finds the refrigerator locked, with a note from Percy on the door, warning that the refrigerator door must never be opened again. Annoyed, Gabe smashes the lock off and opens the door... and finds the severed head of Medusa inside. Fade to black as the snake heads lunge out, and the credits resume.
