The infamous jewel thief the Lone Wolf, who is actually Michael Lanyard, returns to New York City. Upon arriving, Michael breaks into a mansion and steals a string of pearls. Although the house is surrounded by police, Michael escapes and goes next door to the home of Marcia Stewart, who is throwing a costume party. Two of her guests, Liane and her husband Mallison, are actually jewel thieves who are after an emerald pendant she owns. Michael is hiding on her balcony when Marcia takes the pendant off, and after taking the jewel, he takes the mask of a drunken guest and joins the party. Michael asks Marcia to dance and she introduces him to the Mallisons as her friend, Colonel Thompson. Michael is intrigued by Marcia and returns the pendant in exchange for her photograph. Later, star detective Crane, who suspects Michael of being the Lone Wolf, pays him a visit, and Michael remarks that the Lone Wolf will prowl no more, because he has met the woman of his dreams. Then, all of the stolen jewels mysteriously reappear. However, the Mallisons and their accomplice, Morphew, try to coerce Michael to join forces with them, but he refuses and they reveal his true identity to Marcia, who does not care and invites Michael to her home. Hours later, after Marcia has admitted her feelings to Michael, he leaves, and Morphew robs her and frames Michael for the crime. Crane goes to arrest Michael, but instead, Michael locks him in a closet so that he may prove his innocence. Michael telephones Liane and pretends to be Morphew so that he may find out the criminal's hiding place. Michael leaves a flower at the hideout to attract Crane's attention and the detective overhears the criminals argue. After Crane arrests the trio, he notifies Michael of the marriage license bureau's hours of business, and Michael presents Marcia with a new jewel, an engagement ring.