It is March 1943 and the War hangs in the balance . . . At Bletchley Park Tom Jericho, a brilliant young codebreaker, is facing a double nightmare. The Germans have unaccountably changed their U-boat Enigma code, threatening a massive Allied defeat. As suspicion grows that there may be a spy inside Bletchley, and Jericho is suspected, his girlfriend, the beautiful and mysterious Claire Romilly, suddenly disappears.
It was meant to be a harmless stag night prank. A few hours later four of his best friends are dead and Michael Harrison has disappeared. With only three days to the wedding, Detective Superintendent Grace - a man haunted by the shadow of his own missing wife - is contacted by Michael's beautiful, distraught fiancée, Ashley Harper. Grace discovers that the one man who ought to know Michael Harrison's whereabouts...