In a run-down hotel room in Oakland, California, Kyle Niles, a hired killer, relaxes the afternoon away with his cat, despite an unwelcome interruption by Daisy, the precocious teenage daughter of the hotel manager.  He then calmly goes to the City Engineering Department and murders new buildings inspector Carl Adams and his secretary.  Afterward, Kyle retrieves a report written by Adams, which advocates inditing Imperial Contractors, owned by corrupt real estate developer A.T. and his syndicate, for involuntary manslaughter.

At a local diner, Kyle then gives the report, which contends that people were killed when one of Imperial's buildings collapsed due to the deliberate use of faulty steel, to Bahrwell, A.T.'s subordinate, and collects his $1,000 pay.  Following their meeting, the crooked Bahrwell goes to the police and reports the money stolen, claiming the $1,000, for which he has the serial numbers, was taken the night before from the payroll for his Oakland office.

Soon, the police are at Kyle's hotel, as the killer paid his rent with one of the marked bills.  After sneaking out of the hotel, Kyle learns from Danny, a piano player at the diner, that Bahrwell's company is based in Los Angeles.  Meanwhile, Sergeant Stan Lowery, an Oakland police detective assigned to Kyle's case, tries to convince his girl friend, nightclub singer Glory Hamilton, to give up her career, but she insists on going to Los Angeles, where she has a singing engagement.  Aboard the Sentinel Express, Kyle and Glory share the same seat in the tourist section of the train.  Needing unmarked cash, Kyle tries to steal five dollars out of Glory's purse, but is caught.  The young singer mistakenly takes pity on the willowy gunman, however, and even offers him part of her sandwich.

The next morning, Bahrwell awakes in his private compartment on the train to see the sleeping Kyle and Glory, and he hastily reports the "payroll thief's" presence to a porter.  Overhearing the conductor's plan to have the police board the train in Glendale, Kyle abducts Glory and forces her to get off the train with him when it makes an unscheduled stop so that the Los Angeles police can be contacted.  Soon thereafter, Bahrwell is given twenty-four hours by A.T. to find Kyle and kill him.  Mistakenly thinking that Glory is Kyle's girl friend, Bahrwell and his henchman Nichols track the singer to the Ruby Room nightclub, and the lecherous businessman invites her to dinner that night at his home in the North Hollywood hills.  There, Bahrwell demands to know where Kyle is, but Glory insists that she previously did not even know the killer's name, let alone his current whereabouts.  The sadistic Nichols then prepares to torture Glory, only to have Stan, who had been sent to Los Angeles on the case, arrive at Bahrwell's door, looking for his missing girl friend.

Told by Nichols that Glory left an hour earlier, the policeman leaves, but Kyle then appears and brutally beats Nichols during a brief struggle.  Kyle releases Glory from her binds, but before they can leave Bahrwell's home, Stan returns.  After the ensuing chase, Kyle and Glory duck into a Hollywood aluminum factory.  Despite being surrounded by forty policemen, they elude detection by hiding in the factory's air raid shelter.  The killer then offers to release his hostage, but Glory refuses to leave, knowing it could lead to Kyle's capture.  Kyle then horrifies Glory by cold-heartedly telling her how he murdered his abusive father and many others, but the hired killer shows great emotion when he is forced to kill a howling stray cat who nearly gives away their location.  The next morning, Stan discovers Kyle and Glory's footprints outside the bomb shelter, but Glory agrees to act as a decoy to help the killer escape.  Though a Los Angeles police captain wants to arrest Glory for helping Kyle, the singer insists that Kyle is a killer, not a thief, and is acting the pawn for Bahrwell and A.T.

Meanwhile, Kyle sneaks onto A.  T.'s estate, but before he shoots Bahrwell, he forces the crooked businessmen to confess everything about Adams' murder, knowing that A.T.'s dictaphone is recording his statement.  When A.T. tries to recover the incriminating cylinder, Kyle shoots him, then guns down Bahrwell.  The police arrive, and Kyle is mortally wounded in the ensuing gunfight.  Before he dies, however, Kyle looks up to Glory, smiles and hands Stan the recording.