A former private eye lands in hot water when he agrees to protect a government witness.

Chandler, a bored, aging night watchman in Los Angeles, quits his job in order to revive his private detective business. He is approached by two government agents, Carmady and Bernie Oakman, to find a missing artist named Katherine, the one-time mistress of racketeer Melchior. Katherine, who wants to break free of her criminal ties, is set to testify against Melchior in a major case mounted by the government, and the gangster wants to silence her. She is being pursued by one of Melchior's hit men, in addition to Chandler, who is instantly attracted to her, and after the hit man is found dead, she convinces Chandler that she was not complicit. As their romance intensifies, Katherine and Chandler attempt to elude Melchior's men, with Chandler unaware that the crooked Carmady is using him as a dupe to get to Melchior. Carmady hopes to install one of his own men, a double agent known as Kincaid, in Melchior's place after arranging for the gangster's death. Soon, Melchior is murdered and the evidence, which has been manipulated by Carmady, points to Chandler as the killer. In a confrontation with Kincaid, Chandler is wounded but succeeds in killing the double agent. Although his plan is temporarily disrupted, Carmady is still pleased with the outcome and calmly saunters off as Katherine comforts Chandler.