In Western Pennsylvania during the late 1960s, Russian-American steel workers Michael (Robert De Niro), Steven (John Savage), Nick (Christopher Walken), Stanley (John Cazale), John (George Dzundza), and Axel (Chuck Aspegren) are preparing for two rites of passage: marriage and military service.
They are like schoolmates, hanging out in a local bar and enjoying weekends of deer hunting. Michael and Nick are also both in love with Linda (Meryl Streep), who seems to juggle both of the men. But their placid life is soon to be changed after they are enlisted in the airborne infantry of Vietnam.
Before they go, Steven marries the pregnant Angela and their wedding-party is also the men's farewell party.
Nick's girlfriend, Linda, makes breakfast for her father while wearing a bridesmaid's dress. Her father, an abusive and hallucinating alcoholic, is upstairs and alone, having an alcoholic attack and has trashed his room. Linda brings him his breakfast and he hits her, leaving a bruise on her face. She leaves for the wedding.
At the wedding reception, the friends quickly become drunk, dancing and acting obnoxiously. Stan is dancing with his girlfriend when the band's singer cuts in. While he dances with her, Stan notices that he keeps putting his hand on her buttocks. John simply laughs and Stan grows angrier until he marches over and hits his girlfriend. Mike dances with Linda and offers to buy her a beer. The two go to the bar and have a drink together while Nick watches them somewhat suspiciously. The bride and groom leave the party in a decorated car and Mike and Nick chase after them, Mike stripping himself naked as he runs, winding up with Nick in a basketball court.
The morning after, with the car still decorated from the wedding, the men drive into the mountains to go deer hunting. Mike takes hunting very seriously and gives Stan a cold shoulder when Stan can't find his hunting boots. He asks Mike for his extra pair and Mike refuses, having grown tired of Stan's casual attitude and forgetfulness on previous trips.
Though they don't agree with Mike's hard attitude, Mike stands by his principles. The next morning, Mike and Nick go out into the woods (Rachmaninoff's dramatic piece "Praise the Name of the Lord" plays on the soundtrack.) Michael stalks and shoots a deer, bringing it down in a single shot.
The troupe returns to Clairton and they go straight to John's bar. John plays a somber piece on the piano and the men sit mostly silent, contemplating their last night together as a group.
The scene cuts to a mountainous region of Vietnam where a small village is being firebombed by the US Army. Michael is there, lying unconscious among the dead. A North Vietnamese Army (NVA) soldier walks into the village. He finds a small group of survivors, men, women and children, hiding in a hidden bunker. He casually arms a grenade, tosses it in and walks off as it explodes.
Moments later he sees a woman, badly injured, carrying a baby. The soldier mercilessly shoots her. Mike springs up and kills the soldier with a flamethrower. As Mike walks around shooting any surviving NVA soldiers, another unit of helicopters arrive and among them are Nick and Steve. Mike doesn't seem to acknowledge them at first when incoming mortar shells from the NVA begin to hit the village. In the distance, more NVA are approaching.
The three are captured and held prisoner in a riverside prisoner-of-war camp along with other US Army and ARVN prisoners. For entertainment, the guards force their prisoners to play Russian roulette and gamble on the outcome. All three are forced to play; Steven aims the gun above his head, grazing himself with the bullet and is punished by incarceration to an underwater cage. Believing that the experience has broken Steven, Mike considers abandoning him. Nick angrily rejects Mike's idea.
Mike, convincing the guards to let him go head-to-head with Nick in the final round, devises a plan to escape that requires 3 bullets in the pistol and shares his plan with Nick. Mike tells him to go after the closest guy when Mike makes his move. Nick, sensing the increased likelihood of imminent demise finds the plan crazy and protests but, seeing it as their best chance of survival, however slim, Mike pleads with Nick to trust him.
In a final game, Mike successfully convinces their captors use 3 bullets in the cylinder while Nick stalls after being chosen to go first. Mike then volunteers to go first and fires and clicks an empty chamber. With only 2 empty of 5 remaining chambers, an almost-broken Nick has his turn and it's an empty chamber. Mike, enraged by continuous taunting, raises his gun to his head and at the last minute pushes the rifles pointed at him aside while turning the gun on his captors.
With 3 bullets in the 4 chambers left, Mike is able to shoot down 3 captors in rapid succession before grabbing a machine gun and killing the rest. Mike has to pull a raving mad Nick from his continued pummeling of his captor and both escape, taking Steven with them.
The three escape the camp by floating downriver on a tree. An American helicopter rescues them, but only Nick is able to board it. The weakened Steven falls into the river. Mike jumps in after him, and helps him to he riverbank. Steven has broken his legs in the fall. Mike carries him to friendly lines.
The psychologically devastated Nick recuperates in a military hospital in Saigon, where the psychologist concludes he is not fit to remain there due to his all but incomprehensible babbling. After he's released, he tries to call Linda in Clairton but hangs up before the call is connected. He aimlessly searches for Mike in the red light district.
Nick encounters Julién Grinda (Pierre Segui), a champagne-drinking Frenchman outside a gambling den where men play Russian roulette for money. Grinda entices Nick to participate, then leads him in to the den. Unbeknownst to Nick, Mike is in the crowd, as a gambler. Though Mike sees Nick, Nick leaves in a hurry and in a daze and they do not reunite.
Back in the U.S., Mike eventually becomes romantically involved with Linda. Nick and Steven are still missing.
Mike finds out that Steve is alive and has returned, and visits Angela, Steve's wife, to find out where he is. She is consumed by madness and not talking to anyone, so writes down a number for him. It is the number for Steven's hospital, which is a veteran's rehabilitation clinic.
Michael reunites with Steven, who has lost both his legs and the use of an arm and is mentally unstable. Steven reveals that someone in Saigon has been mailing large amounts of cash to him, which Mike suspects is from Nick, who may still be alive. Mike takes Steven home over Steven's protests.
Mike travels to Saigon just before its fall in 1975. With the help of the Grinda, he finds Nick in a crowded roulette club, but Nick appears to have no recollection of his friends or his home in Pennsylvania, appearing instead to be in a constant state of shock.
In a game of Russian roulette in the gambler's bar, Mike and Nick are pitted against each other, in an attempt on Mike' part to have Nick remember his life before the war and his family and friends. Mike's attempts to persuade him to come home are unsuccessful, Nick defiantly raises the gun and shoots himself in the head.
The film ends with Nick's funeral back in America and his friends' response to it. Everyone's there, and even Angela and Steven seem to be on the mend. At the wake they all sing "God bless America", and toast Nick.