The World War II years, filled with espionage and spies of all sorts, were perfect for the foibles of Charlie Chan (Sidney Toler). And in his 1944 venture, America"s Number One Chinese detective is enlisted by the Secret Service to find the person who murdered the inventor of a top-secret device. Charlie takes his time as he investigates the case of a scientist murdered for devising a wayto protect US forces from German U-boats. Bedeviled by a gaggle of eccentrics, his nervous assistant (Mantan Moreland) and his exuberantly in-the-way offspring (Benson Fong and Marianne Quon),Charlie must decide which of a houseful of guests is actually the plan-purloining Master Spy!