Chan and son Lee solve a complicated murdered in New York involving blackmail and a diary exposing racketeering.
On a ship Charlie Chan (Warner Oland) and his son Lee Chan (Keye Luke) help Billie Bronson (Louise Henry) out of her locked room after a man searched her room. Chan tells Lee to stop stealing towels, and Billie asks Lee for an aspirin. Police Inspector Nelson (Harold Huber) greets Chan at the dock, as Billie objects to her photo being taken. Nelson tells Charlie that Billie was wanted as a witness. Reporter Speed Patten (Donald Woods) questions Billie in a taxi, and she promises to meet him at midnight. Joan Wendall (Joan Marsh) sells her photo of Billie to editor Murdock (J. Edward Bromberg) for $100. Billie calls Murdock to make a deal. Lee finds Billie about to enter their room and follows her to the Hottentot Club. Buzz Moran (Leon Ames) sees Billie and tells her to leave town. Lee can't get into the club without a "girl" but asks a Chinese woman to help him. Moran tells Johnny Burke (Douglas Fowley) to keep Billie out of town. Billie argues with Burke and threatens him with a gun.
Chan speaks to police at a dinner; Nelson learns that Billie was murdered and asks Charlie to help. Lee was arrested, but Nelson orders him released. Nelson accuses Burke's girlfriend Marie Collins (Joan Woodbury) of killing from jealousy. Charlie notices differences in a photo of the crime scene. The lights go out, and Burke escapes. The Chans' hotel key is gone. Thomas Mitchell, the man who searched Billie's stateroom, is found dead in the Chans' room. Charlie says Billie hid something in his bag. Marie says Mitchell was her husband. Nelson and the Chans find Murdock in Billie's room waiting for her; he wanted to buy her diary on rackets and politics. Burke's fingerprints were found on Billie's gun. Moran calls on Burke, who hits him and runs out as Moran shoots at him. Murdock tells Patten that Burke turned himself in; but a test finds no gun-powder on Burke's hand. Lee is found in Burke's office and is thrown out.
Burke tries to leave town but is arrested. Murdock gets a special delivery letter and is arrested too, while Moran is also pinched. Patten warns Charlie, and all are gathered at the Club. Chan shows the photo of Burke and Marie. Murdock's letter is a page from Billie's diary that reveals Patten as a blackmailer. Patten calls it a forgery, proving his own guilt. Charlie explains that Patten is the murderer. Patten pulls a gun, but Lee stops him from shooting Charlie.
This stylish and quick-moving mystery offers escape entertainment with a murderer unsuspected until the end.