Inspector Duff works with the Scotland Yard. He is called in to investigate a mysterious murder that occurred at a famous local London hotel. A deaf old man, traveling on pleasure trip from America with his daughter and granddaughter, has been murdered during the night. At first, the investigation seems to be pointing towards Doctor Lofton, the leader of the tour group, as the culprit. Much to the chagrin of the other travelers in the group, they are all subjected to questioning and investigation by Inspector Duff. A few look good for the murder - an infamous Chicago gangster, an exceedingly nervous man, a few people in the wrong place at the time of the murder. Without evidence, Duff is unable to detain the group from continuing on with their tour. He finds himself wishing for the assistance of his old friend, Charlie Chan, who now resides in Hawaii. The plot thickens when one of the suspects is found dead at a further stop on the trip. Duff finds himself traveling to investigate the