Under-Cover Man

New York "man-about-town" Kenneth Mason kills office delivery boy, Jimmy Madigan, with his penknife and steals the bonds he carries. He delivers them to Martoff, a crooked Russian investment broker, who tries to sell them to Sam Dorse, his fence, but when Sam refuses to have anything to do with the bonds because of Jimmy's murder, Martoff kills him. Sam's son, criminal Nick Darrow, offers his services as an undercover man to police Inspector Conklin to discover his father's murderer. Conklin warns him that he is the only one who will know that he is working for the police, and that he will not be able to help him if he gets in trouble. Conklin gives him a letter of reference to Martoff from a crime boss named Patty Kilbane, which they took from a mug who just came into town. Nick uses the letter to impersonate Oliver Snell and introduces himself to Martoff, telling him he has a client who needs some "hot" bonds that will not resurface for fourteen years. Martoff arranges for Nick to meet Mason that night at the Padlock Club. Nick enlists the help of Jimmy's sister, Lora, who agrees to change her name and her apartment and pretend to be Nick's girl to help find her brother's murderer. They quickly becomes friendly with Mason and his girl friend Connie, and while Lora flirts with Mason, who reciprocates the interest, Nick flirts with Connie. Later that night, Nick returns with Connie to her apartment, and when she drunkenly accosts him, he fends her off telling her she should stay true to Mason and keep her mouth shut. Mason has overheard and hits Connie after Nick leaves. Finding Nick's handkerchief, which is monogrammed with Nick's own initial, not those of Oliver Snell, Mason becomes suspicious. Martoff and Mason test Nick by recording his voice and playing the message over the phone to Inspector Conklin. If police respond to this call, hired killer Dannie will kill Nick. No police arrive to help Nick, and he therefore passes the test. When Patty Kilbane arrives, Nick gets nervous, but Patty is mysteriously shot, and is therefore unable to identify him. The next day they pull their bond heist, shooting some guards in the process. In the getaway car, Martoff brags to Nick how he killed Sam. When they switch to a car driven by Dannie, Nick tells him that Martoff met with an accident and he will not be joining them. They return to Mason's apartment, where he has locked Lora in a room after tricking her into confessing to her and Nick's identities. Mason tells Dannie to kill Nick, but Nick fights with them both, and Dannie takes them all hostage. The police arrive, and Inspector Conklin reveals that Dannie is also working undercover for them. Dannie admits to Nick that he killed Kilbane so he would not be recognized, and Conklin invites Nick to join the force if he is ever so inclined. Dannie invites both Nick and Lora to a movie, but they have other plans.