Wartime secret agents Col. Charles Waslow-Carton (Tony Franciosa) and Lt. Col. Philip Braden (Guy Stockwell) infiltrate enemy lines, posing as POWs. Their mission is to destroy a deadly new type of torpedo, hidden in a Nazi stronghold in France. Their contact is Denise Marchois (Anjanette Comer), whom Waslow-Carton had coerced into marrying a German baron (Paul Hubschmid) before the outbreak of war, thus allowing her to continue her spying activities unimpeded. Upon the completion of their mission, Marchois chooses to remain behind with her husband, whom she has grown to love.