Documentary-style prologue follows training of O.S.S. agents for WWII work behind enemy lines. One of the group is a German "mole;" leaders Gibson and Sharkey are aware of this and scheme to feed him false info about the invasion of Europe, while the real agents go to France to find a secret V-2 rocket depot. But the German spy outsmarts them and rejoins his people knowing too much; Bob Sharkey takes the risk of going in after him...