During a bank robbery, a guard is shot and killed by one of the robbers, Harry Wheeler, Paul Richards, who escapes with $250,000.
Lona McLane, Kim Novak, leaves a movie theater and walks to her car. The car won’t start, and Paul Sheridan, Fred MacMurray, appears at her window. He’s unable to fix the car, so he takes her to a bar while a mechanic completes the repair. They spend the night—and the next three days—together, a stretch that will set the tone for what follows.
Next morning, we learn Sheridan is a cop, undercover to befriend Lona in the hope she’ll lead them to Wheeler. The police want Wheeler alive for questioning, and a careful surveillance operation is arranged on Lona’s apartment, with Sheridan, Rick McAllister, Philip Carey, and Paddy Dolan, Allen Nourse, monitoring from a nearby unit. Lieutenant Eckstrom, E.G. Marshall, is overseeing the plan and urging Sheridan to keep Paddy in line, since Paddy is near retirement and coping with a drinking problem that could jeopardize his pension.
As the stakeout unfolds, McAllister keeps a wary eye on Lona’s neighbor, Ann Stewart, Dorothy Malone, who seems to be a quiet counterpoint to the city’s tense mood. One day, Sheridan enters the building and saves Ann from a persistent suitor, which softens the edge of the routine surveillance. Ann’s presence hints at a subtler emotional landscape behind the noir’s brisk procedural machinery.
On a subsequent shift, Lona leaves her apartment, and Sheridan shadows her. She heads to his own place and flatly accuses him of tampering with her car to lure her into the trap, but she soon forgives him, confessing love. She presses Sheridan to kill Wheeler and take the money so they can run away together, but Sheridan remains essentially honest in his instincts and refuses the plan—yet his resolve wavers, and he cannot entirely resist her charm, ultimately agreeing to meet her on the roof to discuss a possible arrangement.
Sheridan’s surveillance partner continues to tail Lona, and McAllister notices Paddy’s car’s phone line goes silent at a critical moment. Paddy abandons his post to visit a bar, raising suspicions. The trio’s loyalties fracture as the case grows more dangerous: Paddy insists they report everything to their boss and hand over the money, even if it costs him his pension, while Sheridan tries to keep the two lives they’ve built intact.
When Miss Stewart, a neighbor, rings the flat for ice during a party, Sheridan answers, and the misunderstanding grows. McAllister and Eckstrom soon realize that Paddy’s absence might be more than a casual lapse, and the tension tightens around the stakeout. Paddy’s mounting suspicions pull him toward a dangerous stand, and a confrontation erupts. In a moment of panic and misjudgment, Paddy moves to his car, a struggle ensues, and Paddy is shot with his own gun. Sheridan uses the moment to stage what looks like a suicide, convincing himself that the pension would have vanished anyway if they’d continued disobeying orders.
Meanwhile, Miss Stewart’s conversation with McAllister reveals that someone saw a man in Lona’s apartment, which pushes the investigators to consider Sheridan as the possible intruder. As Eckstrom and McAllister question Lona, Miss Stewart retrieves her trash and crosses paths with Sheridan in the hall, then rushes to alert the police. Sheridan abducts Miss Stewart and takes her to Wheeler’s car to secure the money, while Lona remains uncertain about what he intends to do next.
With Eckstrom and McAllister returning to the stakeout, the detectives piece together Sheridan’s motive and realize he has both women in his control. They speed toward Wheeler’s car, where a second, unseen police presence blocks the intended escape. Miss Stewart is sent across the street to retrieve the money from the trunk, and when she is warned to stay down by McAllister, she drops to the pavement as gunfire erupts. Sheridan orders Lona to run, hoping to reach the car and a last-minute getaway, but he misreads the field of fire. A different detective waits in the shadows and fires, mortally wounding Sheridan.
As an ambulance arrives, Lona kneels at the dying Sheridan’s side, while Rick leads Miss Stewart away from the dangerous scene, stepping into the night with a cautious, uneasy fate ahead.
