Asian sleuth Mr. Wong gets caught up in the mystery surrounding a policeman's death.

When Detective Dan Grady is murdered while on smuggling detail in Chinatown, his friend Bill Street, captain of homicide, investigates with James Lee Wong, "the Chinese copper." Wong finds a rare jade figurine in Dan's desk and visits Chinatown jeweler Belden, who specializes in Oriental imitations. With the help of female reporter Bobbie Logan, Street locates a witness who saw Dan in the Club Neptune the night he was murdered. The club is run by crooked gambler "Hardway Harry" Lockett, who is part of Belden's smuggling ring. Lockett's moll, Tanya Sarova, wants out of the smuggling ring in order to marry Belden's innocent son Frank. When Belden learns of his son's plans to marry, he threatens to talk if Lockett has Frank killed. That night, Belden is killed in his store, which Wong realizes is filled with smuggled jade. Tanya is then found dead, and Frank is arrested on suspicion of murder. The next morning, Street calls all the suspects to his office, and Frank insists that Tanya was dead when he arrived at her apartment and that the radio had been on. During the interrogation, Griswold, the writer of a mystery radio play which Belden sponsored at the request of his financial adviser, Mr. Forbes, is murdered in Street's office. Wong discovers that the play was aired at the exact time Tanya was murdered and contains a gunshot fired at exactly the time a switchboard operator heard one over the phone. A ballistics report then reveals that Tanya, Belden and Dan were all killed with the same gun. Wong goes to Tanya's apartment and finds Forbes, whom he now knows killed Tanya because she was leaving him for Frank. Forbes had rigged a cord to unhook Tanya's phone so the operator could hear the shot on the radio and place the murder during Frank's visit. Forbes now pulls a gun on Wong, who is saved by Bobbie, and Street arrests the killer.