American officer Strobel, a former actor, and Nobel Prizewinner Professor Aubernet operate behind German lines in Normandy disguised as German officers. Their mission is to disable an intricate system of flame-generating beach defenses prior to the Allied invasion of France. As D-Day approaches, American paratroopers led by Captain Jack Murphy are inadvertently dropped prematurely near the control site for the defenses. Murphy's handful of men team up with Strobel and local Resistance fighter Denise to infiltrate and destroy the German defenses in time for the Allied landings.