The film begins in the drunk tank of a town jail, where Gunnery Sergeant Tom Highway is recounting tales from his military service to fellow inmates. His storytelling takes a turn when another prisoner ridicules his rank, prompting Highway to swiftly disarm and defeat him after a knife is pulled. The following day, in court, the judge grants Highway a final chance after he faces charges for public drunkenness and disorderly conduct, which frustrates the officer whose squad car he vandalized. The cop, dismissive of Highway's military background, taunts him, leading to a quick exchange of insults.
Once back at the base, Highway, who now works in the supply division, declines a bribe from an officer offering him Cuban cigars. He's soon notified of his transfer to Camp Lejeune in North Carolina, where he’ll train a group of unmotivated Marines. During his journey on the bus, he meets Stitch Jones, a young guitarist recently kicked out of a club for starting a fight. Highway finds Jones exhilaratingly obnoxious, particularly when the latter steals his bus ticket during a pit stop.
Upon arriving at Camp Lejeune and reuniting with his old friend Sgt Major Choozoo, Highway meets Major Malcolm Powers, a strict officer with a football background at Annapolis. Knowing Highway's inability to conform with authority, Powers assumes trouble lies ahead. Highway is assigned to the challenging "recon" platoon, filled with unfit recruits who have been abandoned by previous sergeants. Adding to his woes, Highway is partnered with the timid Lieutenant Ring, a bland leader devoid of the backbone needed for their charge.
As Highway encounters his platoon, their initial disdain is palpable. Deciding to shake things up, he destroys their boombox, urging them to have one last night of freedom before his rigorous training begins. Stitch Jones, of course, makes an appearance, prompting Highway to drag him back to pay for the stolen bus ticket. The encounter stirs resentment within the platoon, who conspire to set up Highway by enlisting the help of Swede Johanson, a hulking member currently in the brig.
In search of respite, Highway visits a local bar where he meets Little Mary Jackson, the widow of a Vietnam buddy. She offers him a place to stay, revealing his ex-wife Aggie works nearby, stirring a mix of regret and nostalgia. Highway attempts to reconnect with Aggie but encounters hostility, especially with Roy Jennings, the bar owner who has become Aggie's partner. After an altercation at the bar involving Stitch's performance and a group of heckling Marines, Roy expels both Highway and Jones.
The next day, Highway intentionally disrupts the platoon's slumber, reinforcing the need for adaptability. His style crosses a line when he fires upon them during training with an AK-47, demonstrating the gravity of their responsibilities. Determined to learn about women's perspectives, he secretly studies women's magazines while remaining vigilant about Aggie's relationship with Roy.
Tensions escalate between Highway and his men as Swede challenges him, but after quickly dispatching Swede and calling on him to join the team, Highway begins to earn their respect. He also takes on the role of mentor as he guides his recruits through the rigors of training, even standing by Profile—one of the men—when an accidental discharge nearly gets them all in trouble.
A combat exercise threatens his reputation as Major Powers sets up the recon platoon as live targets for 1st Platoon. Highway, dissatisfied with the lack of preparation, takes matters into his own hands, staging a mock ambush despite Powers' disapproval. Remarkably, Lieutenant Ring covers for him, allowing for a moment of camaraderie amidst the chaos.
Eventually, both Highway and his men find themselves mobilized for action in the 1983 invasion of Grenada. Their mission aims to rescue American medical students amid enemy territory. Despite initial apprehension, Highway encourages improvisation, leading them to subdue enemy positions with unexpected tactics. Amidst the uproar, Highway's leadership sparks a transformation within the platoon.
As the narrative unfolds, Highway's relationship with Aggie becomes a subplot, reaching a climax when he learns of her potential engagement to Roy. Meanwhile, powers within the military landscape shift as Highway takes virtually any opportunity to demonstrate not just his capabilities but also the growth of his men—from uninterested recruits to committed Marines.
In the battle to secure victory for his platoon, Highway confronts Powers about the value of initiative over rigid adherence to Protocol, leaving an impression that resonates throughout the ranks. Ultimately, the story culminates in Hudson's retirement and unexpected moments of reconnection and reconciliation in both his personal and professional life, albeit intertwined with heartbreak and reflections on valor.
In the end, Highway's guidance leads the platoon to succeed in their missions, solidifying their camaraderie and earning recognition upon their return home—a warm reception that includes Aggie, affirming that while the battlefield seems to have changed them, some bonds remain unbreakable.
