Lieutenant Barney Nolan, Edmond O'Brien, a 16-year veteran of the police force, has had it with the world. He once prided himself on doing the right thing, but years on the force have corroded his conscience and sharpened his ruthlessness. In a secluded alley late at night, he fatally shoots a bookmaker in the back and steals his $25,000, then calmly claims he was forced to kill the man because he tried to escape custody. The accusation shatters the trust around him: while Sergeant Mark Brewster, John Agar, his longtime friend and protégé, and Captain Gunnarson, Emile Meyer, believe him, a sharp-eyed newspaper reporter, Cabot, Herbert Butterfield, suspects there is more to the story than a desperate moment of self-defense.
Barney’s personal life spirals alongside the crime. He takes his girlfriend, Patty Winters, Marla English, to tour a for-sale house and hints at a future together—perhaps even marriage. He slips away to hide the stolen money behind the home, then returns to share a tense, intimate moment with her, leaving Patty with the impression that he’s planning a life away from trouble. The plot thickens when Packy Reed, the dead bookmaker’s boss, sends private investigators Fat Michaels, Claude Akins, and Laddie O'Neil, Lawrence Ryle, to confront Barney. After Barney leaves for the meeting, Michaels and O’Neil corner Patty, and Packy gives Barney one chance to return the money—an offer Barney stubbornly refuses.
A crucial witness emerges: Ernst Sternmuller, a deaf-mute man who saw something that night. He approaches the police with a note describing what he witnessed, but does not recognize Barney as the killer. Barney later visits the bookmaker’s apartment to silence Sternmuller, and when the man finally recognizes the killer’s clothing, he refuses money to keep quiet. Barney, furious, pushes Sternmuller, who falls and dies from the impact. The police soon discover that Sternmuller had been compiling a full account of the murder, and Detective Mark Brewster begins to connect the dots that threaten to expose Barney.
Meanwhile, Barney tries to live a nocturnal double life. He swigs at a bar, fending off a flirtatious Beth, the Girl at Bar, played by Carolyn Jones, as he clings to the hope of reaching Patty on the phone. When she finally answers, Patty reveals that Michaels and O’Neil had menaced her, and Barney becomes consumed with rage and a plan to meet the two men and hand over the money. The confrontation at the bar escalates quickly: Barney pistol-whips the two men into unconsciousness, and the crowd erupts in panic as the fight spills into the room.
Back at home, Barney faces an impending reckoning. Mark Brewster arrives to arrest him, and a struggle ensues in which Barney gains the upper hand, nearly shooting Mark in the back before restraining himself. He then goes to Patty to coax her into fleeing with him, insinuating Packy is trying to frame him. For a moment, Patty seems ready to believe him, but a telltale detail about the money unsettles her, and their alliance cracks.
The investigation moves forward as Mark, now in possession of Sternmuller’s notebook, presents the evidence to Captain Gunnarson, and a city-wide manhunt is launched. Barney overhears the radio chatter and slips back into hiding, donning an old patrolman’s uniform to blend in. A shady associate helps him plot a getaway to Buenos Aires, but at a crowded pool he discovers a trap: a bandaged Michaels is waiting, a cruel sign that Barney’s own swindle—the money turned into newspaper clippings—has been exposed by his own misdirection.
A tense shootout erupts between Barney and Michaels, and Barney kills his pursuer. He hurries to the new house to dig up the money he had stashed there, but the indebted city chest closes in. Mark has deduced the money’s hiding place, and as the police converge on the house, Barney emerges from the yard and fires at the officers. Surrounded and outgunned, he is shot dead as the final shot quietens the yard, ending a career that began with ambition and ended in conspiracy and blood.
