In 1967, amidst the tumult of the Vietnam War, a fresh group of recruits from the United States Marine Corps arrives at Parris Island to undergo rigorous basic training. Upon having their heads shaved, they are introduced to their fierce Senior Drill Instructor, Gunnery Sergeant Hartman (R. Lee Ermey), who uses extreme methods to mold the recruits into battle-ready Marines. Among these recruits are Privates "Joker" (Matthew Modine), "Cowboy" (Arliss Howard), and the corpulent, clumsy Leonard Lawrence (Vincent D'Onofrio), who earns the mocking moniker of "Gomer Pyle" as he consistently incurs Hartman's wrath.
Despite the harsh discipline imposed by Hartman, Pyle struggles to adapt, eventually being paired with Joker. With Joker's assistance, Pyle shows some improvement; however, his progress is abruptly interrupted when Hartman discovers a contraband jelly doughnut stashed in Pyle’s footlocker. Viewing this as a major failure, Hartman implements a brutal collective punishment system—every blunder Pyle makes results in punishment for the entire platoon, while Pyle himself is spared. This leads to the platoon enacting a harsh hazing ritual, known as a blanket party, where they restrain Pyle and beat him with bars of soap wrapped in towels. Following this harrowing experience, Pyle undergoes a dramatic transformation and becomes a model Marine. While this impresses Hartman, it raises alarm bells for Joker, who observes troubling signs of Pyle's mental decline, notably his bizarre behavior of talking to his M14 rifle.
After the recruits graduate, they receive their Military Occupational Specialty assignments, and Joker is designated as a Basic Military Journalist. On their final night at Parris Island, Joker encounters Pyle in the bathroom, where he is loading his rifle. Joker’s attempts to soothe Pyle are in vain as Pyle begins to execute drill commands and recites the Rifleman's Creed. The ensuing chaos awakens the platoon and Hartman, leading to a tragic confrontation. In a shocking turn of events, Pyle shoots Hartman dead before turning the weapon on himself.
Fast forward to January 1968, and we find Joker, now a Sergeant, serving as a Marine War correspondent in Vietnam for Stars and Stripes, alongside Private First Class Rafterman (Kevyn Major Howard), a keen combat photographer eager to experience the thick of battle. At the Marine base, Joker faces ridicule for his lack of the thousand-yard stare, a stark indicator of someone who has not seen war. Their routine is shattered with the onset of the Tet Offensive, as the North Vietnamese Army intensifies its assault on the base.
The following day, journalists receive updates regarding enemy advances across South Vietnam, and Joker is dispatched to Phu Bai, accompanied by Rafterman. There, they rendezvous with the Lusthog Squad, where Cowboy has now advanced to the rank of Sergeant. During the intense Battle of Hue, Joker witnesses horror as platoon leader "Touchdown" (Ed O'Ross) is killed in action. Once the area is secured by US Marines, American news personnel enter Hue, questioning Marines about their experiences and views regarding the war.
During a tense patrol, Crazy Earl (Kieron Jecchinis), the squad leader, falls victim to a booby trap, leaving Cowboy in command. As they navigate murky terrain, Cowboy orders Eightball (Dorian Harewood) to scout ahead. However, tragedy strikes as a Viet Cong sniper injures Eightball, prompting squad medic Doc Jay (John Stafford) to break rank and provide aid, only to be wounded himself. Cowboy learns that tank support is unavailable, prompting a call for withdrawal. In a moment of insubordination, Animal Mother (Adam Baldwin) disregards Cowboy's orders and attempts a rescue of the wounded men.
Despite identifying only one sniper in the vicinity, disaster ensues as both Doc Jay and Eightball lose their lives during the confrontation. As Cowboy leads an assault on the sniper’s position, Joker finds himself face-to-face with the enemy—a teenage girl. As his rifle jams, he inadvertently alerts her to his presence, but Rafterman comes to the rescue, fatally wounding her. With the squadnow united, they stand over the wounded sniper, who begs for a merciful death, igniting a moral debate among the Marines. In a moment fraught with hesitation, Joker ultimately pulls the trigger.
The Marines, now congratulating him on his "kill," march back toward camp, singing the Mickey Mouse March. Reflecting on his experiences, Joker muses that even while being "in a world of shit," he is relieved to be alive and unshackled by fear.
