Alden "Bill" Carter III sees a beautiful woman, Jerry, dining alone at the Park Savoy in New York, and after a brief flirtation, introduces himself. After he entreats her to be his "mystery woman" to make his girl friend jealous, Jerry agrees to attend a reception that night with him at the Douglas home. This plays right into Jerry's plans, as she is a jewel thief who intends to steal the Douglas jewels with her cohorts, Uncle John and Jeff. That night at the reception, Bill apparently becomes drunk, and Uncle John, posing as a Swedish waiter, steals the necklace from Mrs. Douglas's neck without notice and gives it to Jerry. Jeff, who is posing as a chauffeur, drives Bill and Jerry to a secluded area where he intends to kill Bill, because he thinks that Jerry gave him the jewels. Instead, Bill robs them, takes Jerry's purse, and forces Jeff to strip and unload his arsenal, which includes guns, knives and a hand grenade. Jerry and Jeff are then arrested for indecent exposure, and upon their release, Jeff and Uncle John intend to retrieve the jewels from Bill at his apartment. After Jerry calls Bill to warn him of their arrival, he appears at her apartment because he correctly assumes that she has the jewels, as they were not in her purse. The police, meanwhile, discover that the real Alden Carter III was playing polo in another state at the time of the robbery. Uncle John and Jeff return to the apartment, and discovering Bill and Jerry together, believe they had plans to escape. Bill and Jerry pretend they are in love to play up to their expectations, and Jerry tearfully promises to return the jewels. In order to avoid doing this, however, Bill attracts a policeman's attention by throwing a statuette out of the window, which hits the policeman on the head and prompts him to come into the apartment. Jerry and Bill are arrested and, while pretending they are a married couple for fun, really fall in love. Upon their release they decide to return the jewels to the insurance company for the reward, however, Uncle John and Jeff find them first. Jerry slips the diamonds into Uncle John's pocket just before they are all arrested by police. At police headquarters, both Jerry and Bill are revealed to be insurance investigators working for different companies because Uncle John had stolen jewels from Mrs. Douglas twice before, and had then split the insurance money with her. Mrs. Douglas promises to refund the money, and Uncle John and Jeff are incarcerated. At the Park Savoy, Bill and Jerry flirt again, this time with the intention of becoming newlyweds.