With just a few hours remaining before the dawn of a new year, Detroit's oldest police station, Precinct 13, is set to close its doors permanently. A minimal team of officers is on duty for the New Year's Eve shift, which includes the troubled Sergeant Jake Roenick (played by Ethan Hawke), seasoned officer Jasper (portrayed by Brian Dennehy), secretary Iris (acted by Drea De Matteo), and the psychiatrist Alex (played by Maria Bello). Roenick is burdened by memories of a failed undercover operation that tragically claimed the lives of his two teammates just eight months ago.
Simultaneously, crime lord Marion Bishop (Laurence Fishburne) finds himself behind bars after a confrontation that results in the death of an undercover cop. He is transported on a prison bus along with three other criminals: the addict Beck (John Leguizamo), the petty thief Anna (Aisha Hinds), and counterfeiter Smiley (Ja Rule). A brutal snowstorm forces the bus driver to divert to Precinct 13, where the prisoners will be temporarily housed until conditions improve.
However, the festive atmosphere at the precinct is abruptly shattered when masked gunmen infiltrate the building, culminating in the death of one prison guard and leaving another critically injured. The officers quickly realize they are surrounded by these attackers, who are preparing to besiege the station. With all cellular and radio communications jammed, an ominous brick thrown into the precinct bearing the name "Bishop" alerts Jasper to the possibility that these assailants might be Bishop's men, coming to liberate him.
This initial theory crumbles when Roenick kills one of the attackers during an assault, discovering a police badge in his wallet. Bishop then unveils the shocking truth: the attackers are actually corrupt policemen led by Captain Marcus Duvall (Gabriel Byrne). Once partners in crime, Bishop and Duvall’s relationship has soured due to Duvall’s greed, leading to a deadly plan to eliminate Bishop before he can testify.
Faced with overwhelming odds against a growing force of street cops, snipers, and SWAT teams, Roenick makes a pivotal choice—to arm the prisoners to help defend the precinct until dawn. While the officers initially harbor distrust towards the criminals, and vice versa, a partnership is forged between Roenick and Bishop as they work together to weather the assault. Their combined efforts allow them to push back the attacking police force and reclaim their lost weapons.
As chaos unfolds, another officer, off-duty cop Capra, unexpectedly arrives, disoriented and fearful. While the precinct's officers are eager to welcome him, Beck is suspicious, fearing Capra may be a police informant. This tension escalates, prompting Bishop to intervene and diffuse the situation before it erupts into violence.
Smiley shares Beck's suspicion, leading them to hatch a desperate plan to escape amidst the chaos outside. The situation intensifies with the explosion of the prison bus, providing a needed distraction for Smiley and Beck. They make a run for it—but tragedy strikes when snipers take out Beck and Smiley as they attempt to flee.
In a further twist of fate, Anna manages to hot-wire a car to escape—alongside Alex—but their plan goes awry. A hidden police officer shoots Anna, resulting in a fatal crash that sees Alex captured. When brought before Duvall, Alex defiantly claims there are "a hundred" people at the precinct, only to be executed, her bravery rewarded with a bullet.
With only Roenick, Bishop, Jasper, Capra, and Iris remaining, their prospects of survival diminish. Bishop soon deduces that a traitor exists among them, suspecting Capra. Before they can act on these suspicions, the police begin bombarding the precinct with renewed vigor.
In a moment of clarity, Jasper recalls an old sewage entrance, leading Roenick and Bishop to take a drastic measure: they ignite the precinct to delay their pursuers. Their escape through the sewer appears successful until they find themselves cornered by corrupt policemen. To everyone's shock, Jasper is revealed to be the traitor—planning to see them eliminated.
In a desperate bid for freedom, Bishop sneaks a flash grenade into Jasper's jacket, triggering chaos that allows the survivors to subdue the officers. Iris and Capra make a frantic escape in an officer’s car, while Roenick and Bishop flee into the surrounding woods.
The chase intensifies when Duvall and his men hunt down Roenick, leading to a confrontation in the forest where Bishop and Roenick are forced to collaborate. Roenick takes the initiative to draw fire, allowing Bishop to pick off their enemies from the shadows. Their plan momentarily succeeds, but Bishop is shot by Duvall, who instructs him to lead Roenick into a trap.
Following a harrowing exchange, Roenick is wounded, yet manages to bring Duvall down in the ensuing chaos. Despite their cooperation, Bishop chooses to spare Roenick's life, hinting at possible future encounters. As officers led by Iris arrive on the scene, Roenick, injured and battle-weary, reassures her when asked if anyone else remains hidden in the woods, stating simply, "no." The final image is of an exhausted Roenick and Iris as they stagger towards an awaiting ambulance, marking the end of a tumultuous night with Roenick remarking, "get used to it."
