Travellers board a flight, unaware that other passengers might be spies and counterspies, complete with secret documents, poison and elaborate plans to engage in international espionage!

All the passengers on an airplane headed for San Francisco are drugged, and when they wake up, it is discovered that a quarter-million dollars is missing. Charlie Chan--and, of course, his #1 son--must discover the identity of the person who doped the passengers and stole the money.