Robert Harris follows up his first novel, the 1992 best-seller FATHERLAND, an account of what Germany would have been like in 1964 had it won the war, with a more conventional spy story. Young Cambridge mathematician Tom Jericho works at the top-secret Bletchley Park, where cryptographers attempt to break the codes created by the Nazis’ Enigma machines and learn the movements of the German army and navy. Failure will likely result in losing the war.

The brilliant but impulsive Jericho is not well liked by his jealous coworkers, but his initial breaking of the Engima code has allowed them to follow German naval maneuvers for weeks. Unfortunately, Jericho cracks up when he falls in love with the beautiful Claire Romilly, who rejects him, and he is sent back to Cambridge. When the Nazis change their Engima settings, Jericho is recalled before he has fully recovered from his breakdown. His efforts to solve the code again and keep a large convoy of American merchant ships from being destroyed are complicated first by evidence that Claire is a spy and later by her apparent murder. He tries to solve three mysteries at once with the able assistance of Hester Wallace, Claire’s roommate.

Harris deals with the relative lack of suspense over the outcome of the war by interweaving the Enigma endeavors with the increasingly complicated Claire subplot and by making an unpredictable neurotic his unlikely hero. ENIGMA, written in an economical, no-nonsense style, is lighter fare than the dark, brooding FATHERLAND and is relatively uneventful until Claire goes missing, but Harris packs considerable action and intrigue into the final third of the book. The novel is also admirable for making what are usually secondary romantic angles central to the weightier plot.