Documentary-style prologue follows training of O.S.S. agents for WWII work behind enemy lines. One of the group is a German agent. 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.