Charlie Chan (Roland Winters) is a private investigator living in San Francisco. One day a Chinese princess comes to visit him in his home. She has just arrived from the East by boat. The princess manages to give Chan’s butler Birmingham Brown (Mantan Moreland) an artifact - an ancient heirloom ring - before she is shot and killed by a poisoned arrow through the window. She leaves a note behind, with the name ”Captain K”. Chan calls for the police to investigate this murder. Bill Davidson (Warren Douglas) with the SFPD comes to Chan, but his friend, the reporter Peggy Cartwright (Louise Currie), also arrives uninvited to the scene.
As Victor Armstrong visits his uncle, Judge Wesley Armstrong, in San Francisco, he is knocked unconscious by an unknown attacker. When he wakes up he finds out his uncle has been stabbed to death. The judge's private secretary, Phyllis Powers, finds the two men and calls the police to the scene. When Victor wakes up he has the knife that stabbed his uncle in his hand.
Manning, owner of the Golden Eye Mine in Arizona, persuades Charlie Chan to help him. To avoid alerting Manning's murderous enemies, Chan registers as a guest at a nearby dude ranch along with his number two son, Tommy, and his black servant, Birmingham Brown. There he meets San Francisco Police Lieutenant Mike Ruark, posing as drunken fellow guest "Vincent O'Brien" to investigate why the mine has suddenly become valuable.
