Pamela Gray goes with Geoffrey Richmond to appeal to the Home Secretary to intervene and stop the planned hanging of her brother Paul, Richmond's former hunt secretary, in three days for the murder of Captain Hamilton of the Royal Air Force, who had been a guest at Richmond's country home at Retfordshire. After the Home Secretary refuses to help, Kemp, his private secretary, instructs Pamela and her fiancé, Neil Howard, to seek the help of Inspector Charlie Chan of the Honolulu police department, who has captured in Honolulu and brought back to London a wanted British criminal. When Neil, who is Paul's barrister, tells Chan that he believes that Paul is guilty, Pamela overhears the conversation and breaks their engagement. Chan, who wants to help, follows her to Retfordshire, where guests are gathered for a hunt. After Lake, the stud groom who, Chan suspects, knows more than he admits, is found dead with a suicide note, Chan, while investigating in the study, is almost killed by a missile from an air-blown pistol. The next day, during the hunt, Chan goes to the Farmwell Aerodrome, where he learns that Hamilton, an inventor, had developed a scheme for silencing war planes just before he died. Returning to the hunt, Chan learns that Richmond's fiancée, Lady Mary Bristol, who had important evidence to tell Chan, had a near-fatal riding accident because pepper was put on her horse's eyes. After Chan tells the suspected guests that the murderer's fingerprints will be on the missing plans, he tricks Richmond into firing at him with a gun filled with blanks as Chan seemingly finds the papers. Richmond is revealed to be a spy whom military intelligence has been following for years. Sometime later, Paul, released, has dinner with Pamela and Neil, who now have been reunited, and Chan.