Michael Lanyard, alias the Lone Wolf and his man Friday, Jamison (Eric Blore), pick up Eve Andrews (Marguerite Chapman), when her car is wrecked. At her place, they discover the body of wealthy playboy Harry Cooper (Gerald Mohr) and are arrested. Inspector Crane (Thurston Hall), who doesn't believe the Lone Wolf has reformed, discovers jewels are missing. Lanyard and Jamison escape. Lanyard learns Cooper was blackmailing Eve, Sonia Budenney (Tala Birell), wife of a famous physician, and Jane Merrick (Mona Barrie), famous actress. He is spotted by gossip columnist Sidney Shaw (Warren Ashe), who agrees not to turn him in if he can tag along. Lanyard learns that Cooper planned to meet a woman at the airport. Hurrying there, he spots the girl and has Jamison trail her. Later, as he is questioning the girl, Patricia (Margaret Hayes), she is shot and wounded. After being turned in twice by Shaw and escaping , despite his promise not to do so, Lanyard and Jamison return again to Patricia's apartment where he learns that she is Shaw's wife.

When an elegantly dressed woman has a flat tire along a country road, Michael Lanyard, the reformed jewel thief known as "The Lone Wolf," and his valet, Jameson, offer to give her a lift. Meanwhile, at a nearby house, Harry Cooper instructs his valet, Arthur, to deliver his suitcase to the airport and then insure that the traveling companion who is to meet him there will be on time. Soon after, Lanyard drops off the woman, Eve Andrews, at Cooper's house. On his way to the airport, Arthur stops to meet two men he has employed to rob Cooper. Explaining that Cooper has been blackmailing some wealthy socialites about their gambling debts, Arthur divulges the combination to Cooper's safe to them. After dropping Eve off, Lanyard discovers that Jameson has stolen her jewel-encrusted evening bag and drives back to the house to return it to her. At the house, meanwhile, Eve is joined by Sonia Beaudine, the wife of a prominent society physician, and Jane Merrick, an illustrious Broadway actress, all of whom are being blackmailed by Cooper. When Cooper retreats to the library to answer the phone, Jane suggests the women band together and defy him. As Cooper examines the jewels he has extorted from the women, the lights go off, a shot rings out and Cooper falls to the ground, dead. By the time Lanyard and Jameson arrive at the house, the women are gone, but Lanyard finds a handkerchief lying next to Cooper's body with the initials "SB" embroided on it. When a passing motorcycle officer notices Lanyard's illegally parked car, he enters the house and finds Cooper's body. After arresting Lanyard and Jameson for murder, the officer summons Inspector Crane of the police department. When Crane arrives, Lanyard sticks a lighted cigarette into a box of explosives that Jameson was carrying, and in the commotion of the ensuing explosion, he and Jameson escape and Jameson pockets the jewels. Realizing that they must find the real murderer in order to exonerate themselves, Lanyard drives back to Eve's deserted car and ascertains her name from the registration card. When Jameson recalls reading a society column announcing Eve's engagement party that evening, Lanyard speeds to the party. There, Lanyard returns Eve's purse, and as he questions her about her presence at Cooper's house, society columnist Sidney Shannon enters the room. Having read about Cooper's murder over the teletype, Shannon threatens to turn Lanyard over to the police unless he gives him the story. When Eve places a surreptitious phone call, Jameson copies down the number and discovers that it belongs to the Balalaika, a tourist nightclub. At the club, Lanyard learns that Eve phoned Sonia, who is dining there with her physician husband. Instructing Jameson to feign being ill to create a diversion, Lanyard pulls Sonia aside and returns her handkerchief. When Lanyard accuses her of murder, Sonia calls for the security guards. Vivian, an old acquaintance of Lanyard, then appears and escorts him to her car, where the thieves hired by Arthur are waiting for him. Thinking that Lanyard is in possession of the missing jewels, the thieves take him to a hotel room. When a search fails to turn up the jewels, the thieves leave Lanyard in Vivian's custody while they return to scour Cooper's house. Tricking Vivian, Lanyard escapes, returns to the club and rejoins Shannon and Jameson. After phoning Crane with instructions to meet him at the Cooper house, Shannon and Lanyard wait in the bushes while the police chase the thieves out of the house and through the neighborhood. After sneaking into the house, Lanyard intercepts a phone call from Arthur and learns that Cooper was to meet someone at the airport. Proceeding to the airport, Lanyard observes a woman reading the headlines about Cooper's death and then hurriedly leaving. Lanyard discovers that she is a guest at the Hotel Cumberland and goes there to interview her. Arriving just in time to witness Arthur demand a necklace from the woman, Lanyard chases him away and begins to interrogate the woman. Just then, a shot rings out, wounding the woman. After summoning a doctor, Lanyard removes one of the woman's calling cards from her desk and then directs Shannon and Jameson to wait for him while he questions Eve. Returning to the engagement party, Lanyard overhears Eve's fiancé, Johnnie Sheldon, tell Arthur that Eve has gone to the Royal Theater to see Jane. When Lanyard insists that Jameson and Shannon wait for him while he goes to the theater, Shannon hands the doorman a note, directing him to alert Crane that Lanyard is at the theater. There Lanyard finds Eve, Jane and Sonia all being held hostage backstage by Arthur. After Lanyard orders Arthur to drop his gun, Crane enters, followed by Dr. Beaudine and Johnnie. Lanyard informs the inspector that all three women were being blackmailed by Cooper and were present at his death, then creates a diversion and flees with Jameson. Back at the wounded woman's hotel room, Lanyard forces the woman to confess that she was in love with Cooper. Soon after, Jameson warns that someone is coming down the corridor, and Lanyard phones Crane and summons him to the hotel. Just then, Shannon bursts in and is about to assault the woman when Lanyard restrains him. When Crane arrives, Lanyard explains that the woman, Shannon's wife Patricia, was planning to elope with Cooper. Learning of his wife's infidelity, Shannon murdered Cooper and then shot Patricia. To insure that Shannon is found guilty, Jameson plants the jewels on him, and when Crane finds them, he arrests Shannon.