The last assassin / Barry Eisler.

Enhanced descriptions from Syndetics:

Barry Eisler has been compared to Forsyth, Ludlum, le Carré, Ian Fleming, and Graham Greene. But his latest thriller brings Eisler into a league of his own. When Japanese/American contract killer John Rain learns that his former lover, Midori, has been raising their child in New York, he senses a chance for reconciliation, perhaps even for redemption. But Midori is being watched by Rain's enemies, and his sudden appearance puts mother and child in terrible danger. To save them, Rain is forced to use the same deadly talents he had been hoping to leave behind. With the help of Tatsu, his friendly nemesis in the Japanese FBI, and Dox, the ex-marine sniper whose good ol' boy persona masks a killer as deadly as Rain himself, Rain races against time to bring his enemies into the open and eliminate them forever. But to finish the job, he'll need one more ally: Israeli intelligence agent Delilah, a woman who represents an altogether different kind of threat . . .