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.

Jeffrey and Glenda are two lovers about to embark on a three-day cruise to nowhere. Their plan is to be married on board by the ship's captain. As Glenda is packing to leave, she receives a threatening phone call from her obsessed, former lover Leo. Glenda confronts Leo and tells him that it's over. Leo, a high-powered attorney calls a hit man to have Jeffrey eliminated. Glenda knocks Leo over the head before he can give the hit man a name. Leo is dead. Glenda sneaks back into her apartment, goes off on the cruise with Jeffrey and pretends that all is swell. Leo's partner, Stephen Bessemer, suspects Glenda and follows her to the ship. Bessemer stages a mock trial aboard the ship and cleverly draws a confession from Glenda. Jeffrey, also an attorney, represents Glenda when she is arrested upon arriving on shore. A skeptical district attorney, and the fact that Jeffrey horsewhips the star witness (the hit man), combine to get Glenda completely off the hook.