Enigma by Robert Harris
Set against the background of an actual historical event, the World War II, Enigma is a thriller that involves mystery of codes and code breaking.
The story revolves around a brilliant young mathematician, Tom Jericho, who works as a codebreaker at Britain’s code breaking centre, Bletchley Park. Shortly after he makes a breakthrough by discovering the key to decode Nazi Germany’s Enigma ciphers, he suffers nervous breakdown and is sent to Cambridge University for sick-leave.
The nightmare begins when the crypt-analysts at Bletchley, discover that Germans have unexpctedly changed their Enigma cipher and the Battle of the Atlantic suddenly hangs in the balance.
In order to save the situation, the authorities turn to Jericho for help. A frantic race to crack the code follows. But it turns out that Jericho has another clandestine enigma of his own to unravel as the woman he is romantically involved with, has disappeared and he suspects there may be a spy in Bletchley.
What follows next is what I intend to leave it to you to find out since I get a commission by Mr. Harris on the sale of his each book =p