A quiet Scottish town becomes the stage for a tangled night of crime, guilt, and supernatural consequence. PC Rachel Heggie (Pollyanna McIntosh) awakens from a nightmare about childhood abuse just before she heads out on patrol, and the night quickly grows more unbelievable. While on duty, she watches Caesar Sargison (Brian Vernel) collide with a mysterious stranger in a collision that leaves the man vanished and evidence of something not quite right. Heggie arrests Caesar, and at the station she is met by Sgt Jim MacReady (Douglas Russell) who charges Caesar with reckless driving. The case expands as Heggie radios PC Jack Warnock (Bryan Larkin) and PC Jennifer Mundie (Hanna Stanbridge) to locate the victim before booking Caesar into cells, where he sits alongside his teacher, Ralph Beswick (Jonathan Watson).
The search leads Mundie and Warnock back to the scene and back to the station with a mute, scratched man who clutches only a notebook filled with lists of names. Heggie calls Dr. Duncan Hume (Niall Greig Fulton) to examine the stranger, but Hume’s reaction is disquieting—he experiences a flashback and nearly kills the patient, convinced the man holds knowledge of dark truths. The unidentified man is found to bear fingerprints of a long-dead old man, and the clues begin to point to something far older and more malevolent. MacReady, too, is thrown by the night’s revelations and orders Mundie and Warnock to place him in cell six, a designation that will become meaningful to the watcher as the film unfolds. Mundie’s own memories surge to the surface, including a brutal beating of a prisoner that hints at a hidden history in the town.
As the night deepens, Mundie and Warnock uncover Hume’s home, seeking his wife, while MacReady drives home, not to rest but to guard the secrets he keeps. Heggie digs into Six’s notebook and discovers the names are all deceased criminals—an ominous pattern that suggests a reckoning is looming. Inside the cells, Six—a figure with unsettling, almost supernatural control—presses Beswick for the truth behind his wife’s beating, and when Beswick’s answers don’t satisfy, Six pushes him toward a suicide attempt. Caesar warns Heggie, and Hume is permitted to examine Beswick, who dies with a final claim to knowing Six.
Meanwhile Mundie and Warnock infiltrate Hume’s house, discovering he has murdered his own family. The police station becomes a stage for another revelation: MacReady is shown to be a serial killer in disguise, a man who seduces and then murders young men, as evidenced by missing posters that adorn the walls. With tremors of fear and guilt echoing through the precinct, MacReady disposes of a dismembered body in his fridge, while the corpse of another victim lies nearby.
Hume helps Heggie carry Beswick upstairs, only to strike at her when the history of his own family spills out. Heggie restrains him and returns him to his cell, while Six hints at a deeper identity tied to the town’s sins. Six reveals he knows about Heggie’s childhood abuse, and when she steps away, he offers Caesar redemption on one condition: confess to a second hit-and-run earlier that night, when a young girl was left to die on the roadside. Mundie and Warnock return to drag Hume into interrogation, a moment that shifts the balance of power in the room.
As Hume confesses to Mundie, Warnock experiences a flashback of staging the suicide tied to the earlier beating. Enraged, Warnock rushes into interrogation and brutally kills Hume, right before Heggie and Mundie, who are powerless to stop him. Heggie’s silence is threatened as the truth about the case tightens its grip on the room. Caesar finally admits to hitting the girl, but Six warns that it is too late for redemption—the girl had died mere moments after his hit-and-run.
Heggie’s own memory returns: Six had distracted her childhood abuser, giving her a chance to escape years ago. Six then reveals Mundie and Warnock’s plan to kill Heggie, forcing her into a fight for survival. She battles Mundie and Warnock, who nearly strangle her, until the dramatic return of MacReady—now unhinged, wrapped in barbed wire, wielding a shotgun and reciting Bible verses. He shoots and kills Warnock, and wounds Heggie and Mundie as they barricade themselves in the station’s cells. MacReady sets the building on fire as Six hints at his true identity—an outcast who seeks a reckoning with humanity’s sins. He offers to help Heggie, but she refuses.
In the escape, Mundie slips and is fatally pierced by broken glass, MacReady pressing the shard further with his rifle butt. Heggie is wounded in the chaos, and Caesar is killed when MacReady shoots him after scarring his face. Desperately, Heggie hurls a fuel can at MacReady, who accidentally ignites it, leaving him mortally wounded and reciting a final Bible verse. With a chilling “Amen,” Heggie ends MacReady’s nightmare with a battering ram, though the fight has left her battered and scarred. She escapes the burning station, and Six appears once more, unscathed, carrying his notebook. He reveals all the names except Heggie’s have been crossed off and condemns the others for their various sins: Mundie and Warnock as adulterers who took justice into their own hands; Beswick as a hypocrite; Hume as cowardly and vicious; Caesar for his weakness and the hit-and-run. Six confesses his love for Heggie and offers her a partner’s place at his side to continue their vigilante justice, and she accepts, sealing a kiss that binds their fates together.
