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Private detective Ted Shane returns to his old partner Ames after he is forced to leave another town.  Ames is not happy to see Shane because he and Mrs.  Ames were in love before she married Ames.  Shane brings business into the agency, however, and one of their new clients is Valerie Purvis, who asks for help finding a man who jilted her.  Ames follows her to a meeting with a man whom she hopes will lead her to her former lover.  The next day both Ames and Farrow, the man he was following, are dead and Shane is the primary suspect.

At Valerie's hotel, Shane demands the true story from her and she forces him out at gunpoint.  When he gets home, Shane finds his apartment and his office have been ransacked, and his secretary, Miss Murgatroyd, has been locked in the closet.  This is all the work of Anthony Travers, an Englishman on the trail of Roland's trumpet, an instrument which is rumoured to be filled with jewels.  Shane suspects that Valerie is also searching for the horn, but she denies it.

Madame Barabbas, a notorious criminal, sends a gunman to bring Shane to her.  She, too, is looking for the trumpet.  Shane takes money from all of them to find the horn, then receives a message to visit a recently docked ship.  When he arrives at the docks, the ship is in flames and Valerie, Travers and Madame Barabbas are watching.

In the confusion, Shane acquires the package containing the horn, which was transported on the destroyed ship, but when he opens it up, sand pours out instead of jewels.  The police round up all the criminals except Valerie.  Shane escapes with her to the train, but before the next station, he accuses her of Ames' murder and delivers her to the waiting police when the train stops.  Miss Murgatroyd is waiting for him and they leave together.