Rain Fall - Barry Eisler

John Rain learned the art of killing as a member of the U.S. Special Forces in Vietnam, and has honed his skills as a for-hire assassin in Japan. He has simple principles - the target must be a principle and never a woman, and he can be the only one hired for the hit. The target always dies from what appears to be natural causes, and in the opening pages of this book, a man has a heart attack in the subway. As John concludes the job, he watches another man diving through the victim's pockets, which starts a cycle of double-crossing that John must resolve before both he and the daughter of the original target wind up dead themselves. It took me awhile to get into the character, but I will definitely follow John through the sequels!