Paul Bruckner, Wesley Addy a surgeon whose license has been revoked for alcoholism, boards a train passing through Arizona under the alias Dr. Sloane. His presence there is part of a caper involving a fictitious patient, and it grants him access to a physician’s bag in the baggage car. There, he blows the safe and makes off with a cash payroll of $500,000, setting the wheels of a tightly choreographed heist in motion. The thieves disembark at a remote small town with a hospital that sits well off any regular train route, and they escape with the money in an ambulance, leaving railroad officials to learn of the robbery only when the train rolls into Phoenix hours later.
In response, the insurance company assigns Charlie Norman, Mark Stevens to the case, forcing him to postpone his Mexican vacation with his wife Ruth the next day. Joe Armstrong, King Calder, a veteran railroad policeman who is also investigating the crime, teams up with him. As the investigation unfolds, evidence surfaces that the thieves stole the ambulance just before the robbery, then ditched it in the desert and escaped in a stolen helicopter, all arranged to a meticulous timetable. Yet one misstep prevents this from being the perfect crime: during the escape, Lombard—the patient who played a key role—accidentally shoots himself, leaving Bruckner and the money trapped with him instead of reaching Mexico and throwing the schedule off balance. The pursuit intensifies as Charlie’s plan to vanish with the loot becomes clearer, and he dreads the unraveling of the scheme.
Charlie reveals himself as the secret mastermind behind the plot, having laid the groundwork after meeting Bruckner and filing a false accident claim. Bruckner, driven by a desperate need for cash, joins in the crime for the payoff. The plan shifts to waiting out the investigation and slipping away to Mexico, but Joe continues to close in, uncovering an accomplice that leads to Wolfe, the owner of the helicopter used in the escape. Realizing that Bruckner and Wolfe have double-crossed him, Charlie kills Wolfe to silence him and makes the death look like suicide. Bruckner, trying to flee across the border with Linda and his share of the loot, panics at a routine customs check and is killed by police, while Linda escapes.
Joe arranges to accompany Charlie to Mexico to track her down, believing she holds the rest of the loot. Charlie sees an opportunity to escape and stashes his cut in a briefcase, intending to slip it into Mexico while suspecting that Bruckner has already arranged to leave with Linda. In the meantime, Ruth has discovered the stolen money and returned it anonymously to the insurance company, having previously attempted a practical joke by hiding fishing gear in Charlie’s briefcase. As the chase escalates, Charlie draws the attention of both Joe and the Mexican police. Cornered and with no viable escape, Charlie and Linda are killed in a final, decisive shootout, and the case closes with the loot effectively lost to the criminals.
