There were two great top secret Allied endeavors during World War II: the Manhattan Project, which developed the atomic bomb in New Mexico, and the program at Bletchley Park, a rural town in Britain, where the finest mathematicians and cryptographers attempted to break the Nazis' unbreakable Enigma code. Winning the war depended on the success of both.

In Enigma, Robert Harris, the best-selling author of Fatherland, transports us to March 1943 and the desperate race against time that was waged at Bletchley. His hero, Tom Jericho, has been called back, while recuperating from a nervous breakdown, to try to crack Enigma before German U-boats sink hundreds more American convoys bringing supplies and munitions to Europe. If he solves the puzzle, thousands of Allied troops will live. If not, Jericho and his peers face the responsibility for a massacre.

When Jericho's ex-girlfriend turns up missing and is suspected of being a Nazi mole, British and U.S. intelligence take frightening steps to plug the possible leak. Everyone is a suspect, including Jericho, who must use his genius - and his heart - to clear both his and his lover's names.