A mystery writer is intrigued by the tale of notorious criminal Dimitrios Makropolous, whose dead body was found washed up on the shore in Istanbul. He decides to follow the career of Dimitrios around Europe, in order to learn more about the man. Along the way he is joined by the mysterious Mr. Peters, who has his own motivation.

Japanese spies attempt to subvert America's war effort; G-Men attempt to thwart their plot.

Joan Bannister is the wife of globe-trotting war correspondent David Bannister. Returning to the US, Bannister becomes suspicious when Joan begins keeping company with known Nazi functionaries, notably the sinister Mr. Peter. Suspecting that his own wife may be the elusive “Madame Spy” wanted by American authorities, Bannister is in for quite a few surprises.

On December 6, 1941, Captain Yamanada of the Japanese aircraft carrier "Hiranamu", orders full steam ahead for Pearl Harbor. His ship encounters and sinks an American yacht and the single survivor, Sue Curry, is rescued by an American submarine, the "Sea Serpent", commanded by Commander Chris Warren. He hears her story and attempts to radio a warning to Pearl Harbor. Yamanada, hearing the signals, orders the airlines jammed, and then sends his son into the air to sink the sub. The attack fails, after the sub makes a crash dive, but they fail in their warning attempts. The next morning, December 7th, the men on the sub hear the story of the bombing of Pearl Harbor, and devise a desperate plan to sink the Japanese carrier by letting the carrier know their position. The carrier comes in search of the submarine.