Charlie Chan, of the Honolulu police, and Inspector Fife of Scotland Yard tour the offices of the New York Police Department with Inspector Flannery, in order to study New York police methods. While dining at a Chinese restaurant, Fife receives a phone call informing him that Sir Lionel Grey, former chief of Scotland Yard, has dropped dead in the offices of Barry Kirk in Wall Street, which was his base of operations. Fife, Flannery and Chan go to the crime scene, and Kirk informs the group that, before his death, Grey was about to solve a big murder case and had invited several guests to a party; he had left the party to take a phone call in Kirk's office and then died mysteriously. The doctor assures the group that Grey died of a heart attack, but Chan notices a dead cat in the room and surmises that the same substance killed them both and that Grey was indeed murdered. The assembled guests are queried, and all seem to be hiding something. In the office, the police discover that the safe has been robbed -- a possible motive for the crime -- and learn that John R. Douglas, a chemical manufacturer, had made the last phone call to Grey. Chan decides to stay on for the investigation. At a café, Shirley Marlowe meets with John, and he tells her that Grey demanded to know the whereabouts of an Alan Raleigh and threatened to take Shirley, Raleigh's former lover, back to England as an accessory to murder if John would not give the information. John then asks Shirley to marry him. After an interview with one of the assembled guests, Chan is led to Shirley, who confesses to Chan that she fell in love with Raleigh before she discovered the crime that he had committed, which Grey was investigating. When informed, Shirley fled, and she has been pursued by Scotland Yard ever since. Chan promises to keep Shirley's secret and goes to find Li Gung, Raleigh's houseboy. Back at Kirk's office, it is revealed to Kenneth Dunwood, another guest on the night of the murder, and Kirk that gas masks were found at John's chemical factory, which implicates John. Shirley sends a letter to Chan, indicating her plan to tell the police everything. As Shirley prepares to go to the station, an unidentified man drops a gas bomb in her car in an attempt to poison her, but the bomb kills her chauffeur instead. At the station, John is brought in, and he denies his acquaintance with Shirley until she tells him that she's confessed everything. He informs the group that he saw a "Chinaman" enter the building with a basket the day he met with Grey. Chan goes again to Li Gung's home, and the former houseboy tries to kill him with a cleverly designed hidden gun, but a black cat upsets the setup, and the gun shoots Li Gung instead. At the check-in room of the Cosmopolitan Club, Chan discovers Grey's briefcase, which he ascertains from the register was checked in after the murder. He calls Fife and Flannery to watch with him who retrieves it, and the trio are surprised to see Kirk claim the important item. At Kirk's office, the crime solving trio wait with the members of the original party, plus Shirley. When Kirk arrives, Flannery instructs him to answer the door and pretend to be alone. Dunwood enters and thanks Kirk for getting his briefcase. Kirk asks Dunwood when he got his membership card to the club, and it is revealed that Dunwood had not been to the club that day as he had said, but had dropped the case off just after the murder. Shirley identifies Dunwood as Alan Raleigh, and Dunwood grabs Chan's unloaded gun and covers the group, but Chan quickly subdues him. The lovers, John and Shirley, embrace as Fife announces that Scotland Yard will close the case. The men shake hands and Flannery commends Chan on his crime-solving brilliance.