Plot

Two murders are committed and a $50,000 Chinese Mandarin stamp is stolen, passed around and eventually recovered as a group of valuable stamp counterfeiters is uncovered, through the investigations of Ellery Queen.

A very rare and priceless Chinese postage stamp is stole as its thief claims two victims in a hotel,, both of whom are murdered in inexplicably locked rooms. Young Ellery romances the stamps beautiful owner, Josephie Temple, while working with his father, Inspector Queen to solve the baffling case and expose the killer.—duke1029

When Jo Temple arrives in Manhattan to sell a rare Chinese Mandarin stamp to collector Dr. Alex Kirk, it is stolen from her hotel room, after which an engraver named Craig is found shot in Kirk's library with Jo's envelope in his hand. Later, Kirk's nieces, Irene and Martha, try to convince him to give Irene her inheritance as soon as she marries Donald Trent, but he refuses. When Ellery Queen, a detective novelist who has fallen in love with Jo, finds her accused of Craig's murder, he is determined to help his father, Inspector Queen, find the real murderer. When the inspector opens Jo's envelope and, instead of the stamp, finds an "I.O.U." for $500,000 from Trent to Craig, Queen accuses Trent of conspiring with the dead man to steal the stamp and then murdering him. Martha then places the stolen stamp on a letter, which is mistakenly mailed. While searching Craig's apartment, Ellery and Jo discover counterfeiting dies and a Rowan and Co. stamp catalog, implicating Howard Bronson, the company's representative who earlier had offered to buy Jo's stamp, in counterfeiting. To allay Irene's fears that Trent is the murderer, Martha tells her sister that she and Trent stole Kirk's stamps and, finding them counterfeit, hoped to employ Craig in restoring their pilfered inheritance by duplicating the Chinese Mandarin. Ellery and the inspector, overhearing Martha, force her to reveal the name of the real murderer, but before she can, she is shot dead. With Martha's evidence that Kirk was also involved in the counterfeiting ring, Ellery solves the murder. According to Ellery's deductions, Kirk, who was seated at his desk behind the library's locked door following the murder, had shot Craig, then locked the door with the weight of Craig's body. Craig had walked into a murder trap meant for Jo. A postman then returns the Chinese Mandarin; the inspector offers his son a partnership in his detective agency; and Ellery proposes to Jo.