Inspector Duff of Scotland Yard visits Charlie Chan in Honolulu to enlist his aid in trapping a strangler who is lurking among ten members of a world cruise being conducted by Dr. Suderman. Before the inspector can divulge his plan, however, he falls victim to the strangler, and Chan begins his own investigation into the murders. His first stop is a visit to the members of Suderman's party, but when he arrives at the hotel, he finds that another murder has just been committed. The victim, Kenyon, is discovered with a bag containing thirty pieces of silver, and Chan deduces that the man was killed in the room of fellow passenger Gerald Pendleton and his body dragged into Kenyon's room. Chan meets the remaining members of the party when Susie Watson screams upon sighting a man on her balcony, and the group assembles in her room to discover that there is a killer in their midst. In addition to Suderman, the party consists of Kenyon's nephew Dick, Susie's secretary Paula Drake, playboy James Ross, Professor Gordon, an archaeologist, the jumpy Gerald Pendleton and the puritanical Mr. and Mrs. Jeremiah Walters. In a panic, they resume their voyage to San Francisco, and amid a sea of false clues, they share a rather uneventful cruise until Pendleton is murdered on the night that the ship is to dock. Chan finds the traces of a warning that Pendleton had wired to his wife, and deducing that the murderer was absent from the farewell party held at the time of Pendleton's demise, Chan begins to develop negatives from the pictures taken during the party, but the killer steals the evidence. As he flees, the murderer is shot and unmasked as Ross. However, Chan remains skeptical, and at the coroner's inquest, he produces Mrs. Pendleton, who explains that the killer is her demented, vengeful ex-husband and that Ross was only his accomplice. Chan then tricks Gordon into trying to kill his ex-wife, thus exposing him as the true murderer.