A U.S. Navy captain and his crew are just beginning to enjoy 48 hours of leave when they receive word to immediately return to duty. On a top-secret assignment, they must disguise themselves as Nazis and infiltrate a severely damaged Nazi U-boat. Once on board, they are to steal the Nazi's top-secret decoding device and sink the sub before the Germans catch on to what's really happening. Their mission is more dangerous and frightening than anything they could have ever imagined, but one which has the power to turn the tide of battle.