In an intense display of strategy and misdirection, four figures disguised in identical uniforms and armed to the teeth converge on the downtown 6 train, the Pelham 1-2-3, at different points throughout its route. Each of these operatives, known as Mr. Blue, Mr. Green, Mr. Grey, and Mr. Brown, quietly take their places among the oblivious passengers, which include an undercover police officer and the train's conductor. With swift precision, they seize control of the train's front car, holding 18 innocent civilians hostage.
Over the radio, Mr. Blue engages in a tense dialogue with New York City Transit Police Lieutenant Zachary Garber, making a hefty demand for $1 million in ransom—equivalent to approximately $4.8 million today—to be delivered within an extremely tight timeframe of an hour. As the stakes rise, Mr. Blue ominously warns that if they do not comply, one hostage will die for every minute of delay. Mr. Green contributes to the chaos with intermittent sneezes, each met with Garber's good-natured "Gesundheit," injecting a strange levity into a grave situation. Throughout this standoff, Garber and his team meticulously plot their next move, speculating on the hijackers' possible escape routes while working urgently to stay one step ahead.
Garber, astutely observing human nature, deduces that at least one of the hijackers is likely a former motorman, as indicated by their skill in decoupling the train's first car and parking it below 28th Street. Amidst the escalating tension, conversations among the hijackers reveal Mr. Blue's troubled history as a British Army colonel turned mercenary in Africa, Mr. Green's tumultuous past involving a drug bust, and the fraught relationship between Mr. Brown and Mr. Grey, who had been expelled from the Mafia for erratic behavior.
The situation spirals when Mr. Grey fatally shoots transit supervisor Caz Dolowicz, adding urgency and violence to the already precarious standoff. In a clever ploy to gain time, Garber deceives Mr. Blue, claiming that the ransom is at the station entrance, merely needing transfer to the train.
As the clock ticks down, a police motorcycle arrives, carrying the essential ransom, while two officers navigate the dark tunnel with the funds in hand. However, just as they near the stalled train, chaos erupts—gunfire rings out from a police sniper aimed at Mr. Brown, prompting a deadly exchange. Tragically, Mr. Blue executes the conductor in the midst of the turmoil.
With the ransom in their possession and split among the hijackers, Mr. Blue orders Garber to restore power to the subway line, ensuring clear paths for their escape. Just as the plan is set into motion, Mr. Green deftly maneuvers the train further south, heightening Garber's alarm and demonstrating the hijackers' calculated strategy to increase their distance from pursuing police.
As the hijackers' dark ambitions unfold, they cleverly bypass the dead man's switch, allowing the train to hurtle forward without a conductor. Meanwhile, John Garber collaborates with Inspector Daniels above ground, successfully halting the train's deadly advance. Unbeknownst to the hijackers, an undercover officer conceals himself between the tracks, ready for a counter-strike as Garber and Daniels pursue close behind.
Tensions escalate back at the crime scene as Mr. Grey refuses to relinquish his weapon, resulting in a fatal confrontation with Mr. Blue. The standoff culminates in tragedy when Blue shoots Grey, only for an undercover officer to launch a swift offensive that leads to Mr. Brown's downfall. In the midst of the chaos, Mr. Green escapes unnoticed through an emergency route.
As Garber begins to decode the hijackers' strategic maneuvers, realizing they must have evaded the dead-man feature, he races to the previously stalled train, using the emergency exit. There, he confronts Mr. Blue just as they prepare to inflict harm on the undercover officer. With no escape in sight, Blue makes the disastrous choice to end his own life against the electrified third rail.
Meanwhile, the Pelham 1-2-3 surges through the southbound tunnel at breakneck speed, triggering automatic safety protocols as it spins into the South Ferry loop. The train screeches to a halt, leaving the hostages shaken but ultimately unharmed.
In the aftermath, Garber deduces that none of the deceased hijackers were actually motormen. His investigation leads him to Green, the last remaining survivor from the crime, as he narrows down leads from recently discharged motormen. Knocking on the door of Harold Longman (Mr. Green), he finally finds his suspect. Longman attempts to feign innocence, but Garber's determination to return with a search warrant hangs over him. As Garber turns to leave, Longman sneezes, eliciting a habitual "Gesundheit" from Garber—a reflexive act underscored by a persistent, scrutinizing gaze that leaves no room for misinterpretation.
