Based on a play by Gina Kaus and Ladislaus Fodor, on the brink of war in Paris Chan uncovers foreign agents smuggling out arms.
On the verge of war with Germany Paris restricts outdoor lighting. Belescu (Noel Madison) is shipping contraband munitions, and Charlotte Ronnell (Dorothy Tree) demands the clearance papers but gets blank paper. Police Prefect Romaine (C. Henry Gordon) is brought Petroff's letter by his butler Antoine (Pedro de Cordoba). Charlie Chan (Sidney Toler) notes that it was opened before. Marie Dubon (Lynn Bari) buys a ticket to Panama from Louis Santelle (Leo G. Carroll). Chan helps Marcel (Harold Huber) follow her. She gives the ticket to Tony Madero (Richard Clarke); but he says he is innocent. Marie goes to Santelle for a false passport, but he demands 50,000 francs so she will have to go to Petroff (Douglass Dumbrille) for money. Antoine's son Philip is going to war, which Petroff mocks. Belescu calls Charlotte that he sent the papers to Petroff.
Marie calls Romaine that Petroff was murdered. Chan helps the blustering Marcel investigate. A camellia is found, and Antoine says that Belescu wore one. Chan finds a broken window in the cellar and evidence of two men drinking brandy. Chan and Marcel find the men in a cafe; they say they gave the loot to Lola but saw a woman there. Charlotte escapes. Marie gives Tony the passport. Chan and Marcel go to the hotel of Marie and question her and departing Tony. Chan figures out that Tony sent the letter threatening Petroff. Marcel has Marie and Tony arrested. In their room Chan finds Santelle's card and goes to him to ask about the passport; but Pierre (Lon Chaney Jr.) knocks him out. Santelle calls to warn Petroff, but the call is forwarded to Marcel. Police see a light and break in to find Chan tied up.
Antoine, Lola, and Belescu are brought to the police station, and Chan brings in Santelle. Chan learns that Marie went to Petroff and that she knows he is dead. Antoine says that Petroff was already dead. Antoine accuses Belescu of betraying France. Belescu says he was shipping fruit, but Marcel finds 400,000 francs on him. Planes are heard, and the lights go out, enabling Belescu to escape. Chan and Marcel learn of Petroff's last telegram and hold the ship. Belescu goes to Charlotte, who shoots him. Belescu tells Chan she is a foreign agent shipping munitions with Petroff. They chase her car. Charlotte gets in a plane that crashes and burns. Romaine commends Chan for exposing the spy ring. Chan says that Antoine killed Petroff to defend his country. Antoine says how and why he did it. Romaine says that there will be no war because of the invitation to Munich; but Chan is skeptical it is a trap.
This mystery reflects the imminent danger felt in France
on the verge of war and suggests that shipping weapons to enemies
is worse than murder.