At his 5th Avenue salon, Henry Woodruff has a special party to debut his new collection of jewelry. At the bar, guest Joan Matthews meets Gregg Dunn. During the show, Sarah Sorrell, modeling a $50,000 necklace, faints and upon her revival, the necklace is missing. Policeman Pat O'Farrell is quickly on the scene and demands that each person be searched for the necklace. Woodruff refuses to force such indignities upon his customers and allows many, including Joan, to leave unsearched. Gregg, an insurance investigator, follows Joan, who has the stolen necklace in her purse. Joan then goes to The Sherrington, a hotel for women, and checks in, claiming to be a battered wife. Jenny, the maid, arrives and discovers a gun in Joan's purse. She tells Francine, Emmy Lou and Happy, women who live on the same floor of the hotel, that Joan is a gun moll, but her claims are dismissed. At the Jeweler's Indemnity Association, Gregg tells his boss, George Grayson, that he knows Joan stole the necklace but cannot prove it; however, he is sure she will contact them to ransom back the necklace for its partial value. Joan does call and Gregg meets her for dinner. During the evening, Gregg tries to talk business, but Joan is more interested in dancing. When Woodruff arrives with Sarah, Joan calls them over. Then, while the two women are in the ladies' room, Woodruff questions Gregg about the necklace. It seems Gregg, Woodruff and Sarah are in cahoots, as Gregg was supposed to steal the necklace himself, but was beaten to it by Joan. Once alone with Gregg, Joan offers to go into a partnership with him. Spotting a drunken matronly lady, the two decide to rob her apartment. The robbery goes as planned until the butler wakes and Gregg shoots him. Back at Gregg's apartment, two policemen arrive to arrest Gregg for murder. When Joan refuses to cooperate, Woodruff enters and informs her the robbery and shooting were a ruse to test her, and asks her to join their gang. The next day, Joan, who is actually an undercover policewoman, meets with police commissioner Vincent Brady. Joan's job is complicated by the fact that she and Gregg have fallen in love. Woodruff, realizing the police are near, decides to move the gang to another town. Joan, however, proposes one final job-- stealing the famous Cavendish rubies. Joan steals a duplicate of the rubies from Judith, another girl at the Sharrington whose fiancé designed the original piece and gave her a duplicate. Later, at Lanton's salon, Gregg watches as Joan steals the rubies. Back at the Sherrington, Judith discovers her jewelry missing, just as maid Jenny learns of the robbery at Lanton's. Listening in on Joan's phone calls, Jenny and the girls become convinced she is a jewel thief, and Jenny calls her boyfriend Pat, the policeman. Sarah, who also lives at the hotel, is told by Jenny that Joan is a thief, part of "Brady's gang." Sarah calls Woodruff, informing him that Joan is a policewoman. Woodruff prepares to leave, while Gregg goes to the Sherrington to take the rubies from Joan. Joan is held prisoner by the girls until they discover Brady's card in her purse, informing them of her true profession. Gregg arrives, strikes Joan and takes the rubies just as Pat appears. Pat shoots Gregg, who dies in Joan's arms. On a train to Mexico, Joan reads the headlines about the end of the jewelry ring and orders a double martini, which she and Gregg always drank together.