Five years ago, one of the wealthiest businessmen in America was assassinated by a professional sniper who was never caught. Now, the dead man's brother has finally tracked down the killer. The assassin, a man known only as Kelton, has retired and is happily married, living on the outskirts of London, his past buried and forgotten. But when a bomb explosion kills Kelton's wife and maims his daughter, the past comes flooding back, and now it is Kelton's turn to seek revenge -- with the help of the British government's super-secret intelligence agency, the Government Communications Headquarters, and its American counterpart, the National Security Agency.