England 1943. Much of the infamous Nazi Enigma code has been cracked. But Shark, the impenetrable operational cipher used by Nazi U-boats, has masked the Germans' movements, allowing them to destroy a record number of Allied vessels. Feeling that the blood of Allied sailors is on their hands, a top-secret team of British cryptographers works feverishly around the clock to break Shark. And when brilliant mathematician Tom Jericho succeeds, it is the stuff of legend.