Spring, 1941. The armies of the Reich are masters of Europe. Britain stands alone while Hitler's submarines prey on the Atlantic convoys that are the country's only lifeline.
As the Blitz reduces Britain's cities to rubble and losses at sea mount, interrogator Lieutenant Douglas Lindsay becomes convinced Germany has broken British naval codes. But he's a lone voice, and his superiors don't trust him. In one last desperate throw of the dice, he sets a trap for his prize captive - the U-boat commander who sent his ship to its doom.