In the fall of 1938, the great powers of Europe struggle to halt the encroaching war by convening at a conference in Munich. As the peace of Europe hangs in the balance, American detective Charlie Chan is drawn into the conflict when Petroff, a foreign agent, is murdered during a Paris blackout. As Chan's investigation progresses, he narrows the suspect list to Tony Madero, a man whom Petroff had framed for forgery because he had objected to Petroff's unwelcome attentions to his wife, Marie Dubon; Alex, Max and Lola, three burglars who had broken into Petroff's house on the night of the murder; Belescu, Petroff's business partner; Louis Santelle, a locksmith in the business of forging passports; and Antoine, Petroff's French butler. When Chan discovers that Petroff died while dictating a telegram about obtaining clearance papers for a special cargo, he begins to suspect that Petroff was a foreign agent dealing in munitions. Chan then traces Petroff and Belescu to Charlotte Ronnell, the head of a spy ring that was shipping munitions to the enemey. After a high speed chase, Charlotte dies in a fiery plane crash, and Antoine admits that he killed Petroff to protect France.