After dining at the home of friends Joan and Bill, stock salesman Joe Downey declines an offer to be driven home, and walks to the nearest bus stop. On the street, Knuckles Morgan, a gunman working for a gangster named Nails, mistakes Joe for James "Slats" Slattery, a man he was sent to kill, and knocks Joe unconscious. Joe revives in a jail cell and telephones Bill and Joan to pick him up. A few days later, Joe returns to the scene of the assault and asks some of the neighborhood residents if they know the intended victim. During his search for Slats, Joe falls in love with Marion Roberts, an attractive insurance claim investigator. While standing outside a drugstore, Joe sees Knuckles and immediately calls police lieutenant Madigan, Knuckles, however, disappears before the police arrive. Later that night, while driving with Marion, Joe sees Knuckles walking down the street and stops his car. Moments after following Knuckles into an apartment building, Joe discovers Knuckles on the floor with a knife in his body. When a neighbor sees Joe standing over the dead man, she calls the police and has Joe arrested. Madigan believes that Joe is innocent and releases him, but not before offering to place him under protective custody in case Slats tries to find the witness to the murder. Joe refuses the lieutenant's offer, and vows to continue his own investigation into Slats's operation. The following day, when Joe's picture appears in the newspapers and his name is connected with the murder, his employer, C. W. Sloan, fires him. Marion, meanwhile, discovers that Slats worked as a shipping clerk at a fur company that was recently robbed, and that he lives in the building where Knuckles was murdered. Suspecting that Slats was somehow involved with Knuckles and his gang in an insurance racket, Marion decides to rent an apartment in Slats's building and search for more clues. One day, while leaving Marion's apartment, Joe is forced into a car and taken to Nails, who is relieved to discover that Joe is not a detective, and that he is only searching for his assailant. The gangster lets Joe go with a warning not to meddle in his business, but assigns one of his men to follow Joe as a precaution. Marion, meanwhile, discovers one of the stolen furs in Slats's apartment, and befriends the gangster to learn more about him. She later accompanies Slats to a nightclub, where she gets into a fistfight with Slats's jealous girl friend Sally O'Brien. Sally finds Marion's badge during the fight, and later reveals Sally's identity to Nails and Slats. Nails orders Slats to kill Marion at their hideout, but Joe and the police arrive in time to save her. With the gangsters on their way to prison, Joe and Marion resume their romance and plan to marry.