Private detective Michael Shayne is hired by cantankerous widow Mrs. Murdock to find a valuable coin known as a brasher doubloon, which she believes was stolen from her collection by her daughter-in-law, singer Linda Conquest. Mrs. Murdock also wants Shayne to arrange for a divorce for her son Leslie and Linda. During the visit, Shayne becomes intrigued by Mrs. Murdock's nervous secretary, Merle Davis. Afterward, Shayne contacts coin dealer Elisha Washburn, who had tried to buy the brasher doubloon, and arranges to meet him later that day. Shayne then visits Lois Morny, one of Linda's best friends, and finds her in the company of Louis Venter, a well-known gigolo. Lois flirts with Shayne but refuses to tell him anything about Linda, and after he departs, he accosts a man who has been following him since he left Mrs. Murdock's home. The man is George Anson Phillips, who claims to be a private detective working for Linda. Shayne agrees to go to Phillips' apartment later, then during his meeting with Washburn, implies that Washburn purchased the stolen coin in order to sell it back to Mrs. Murdock. As he departs, Shayne overhears Washburn call Phillips, and when he arrives at the detective's apartment, he finds that Phillips has just been shot to death. That evening, Shayne goes to the Idle Valley Club, which is owned by Lois' husband Alex. It is also where Linda works, and Shayne is finally able to meet her. Linda indignantly declares that she did not steal the coin, and does not want any of Mrs. Murdock's money to make her divorce Leslie. Linda asserts that she never heard of Phillips, after which Shayne learns of a connection between Venter and Phillips. The next morning, Mrs. Murdock tells Shayne to drop the case because she found the coin in a dressing gown pocket, but Shayne becomes suspicious when he receives another brasher doubloon that was mailed to him by Phillips before he died. When Shayne takes the coin to Washburn's office for identification, however, he learns that Washburn, too, has been murdered. Washburn's secretary throws suspicion onto Shayne, and police lieutenant Breeze gives him six hours to clear himself. Shayne goes to Mrs. Murdock's home, where she admits that her coin is a counterfeit and Leslie confesses that he stole it to use as collateral for a gambling debt he owes to Alex. Shayne learns that a dental supplies company had been sending Venter materials that could have been used to counterfeit coins, but before he can question Venter, an hysterical Merle confesses that she killed him. Merle admits that she had been giving Venter money for eight years, but refuses to say why he was blackmailing her. Shayne leaves Merle, whose gun has not been fired, in the care of Linda, then goes to Venter's apartment. Soon after, Breeze determines that the gun used to kill Venter was used to kill Washburn and Phillips as well, and Shayne asserts that Venter, who was counterfeiting the coins with Washburn, Phillips and Leslie, shot the other two and was in turn killed by Leslie, who was trying to protect his mother. Shayne reveals that Merle had been Mr. Murdock's secretary until eight years ago when he made advances to her while drunk. In shock and hysterical, Merle did not realize that Mrs. Murdock had entered the room and then pushed Murdock out a high window to his death. Venter, who was photographing a parade below, accidentally took a picture of Mrs. Murdock committing the murder and has been blackmailing her ever since. Leslie killed Venter when he threatened to expose Mrs. Murdock, who had convinced Merle that she was to blame for Murdock's death, once and for all. Just then, Breeze learns that Mrs. Murdock choked to death, and with Leslie in custody, the case is closed. Later, Merle returns to her home in the Midwest, and Linda promises to see Shayne after she obtains a divorce.