The Amateur (Penguin Modern Classics – Crime & Espionage) by Robert Littell

Charlie Heller is a CIA cryptographer, a quiet man in a back-room job. He’s not a spy, let alone an assassin. But when his beloved fiancée is murdered by terrorists and his employers refuse to pursue her killers, Heller decides to take matters into his own hands. Pursuing the culprits all the way behind the Iron Curtain, he is playing a dangerous game and doesn’t know the rules. But even an amateur can outwit his enemies – especially when he’s got nothing to lose.