Although this is a Charlie Chan book, Charlie doesn't actually show up until the second-half of the book. Rather, Inspector Duff of Scotland Yard, whom we met in Charlie's third adventure in San Francisco, is the major protagonist in the first-half of the book.
A member of a party on a round-the-world tour is murdered in a London hotel. Inspector Duff investigates, but can't pin the crime on any of the members of the party and eventually has to let them continue on with the trip. Duff gets leave to join them and continues around the world with the tour through the middle east, India and south east Asia. He's still with them by the time they get to Hawaii, by which time several more murders have happened. While consulting with Charlie, Duff himself is shot (not fatally) and Charlie takes over the investigation. Charlie, of course, figures things out on the 6-day voyage from Hawaii to San Francisco.
I dunno, this was a decent enough book, but I don't think it was as good as the first few books in the series, nor the last one for that matter.