Zero Sum — Barry Eisler

Returning to Tokyo in 1982 after a decade of mercenary work in the Philippines, a young John Rain learns that the killing business is now controlled by Victor, a half-Russian, half-Japanese sociopath who has ruthlessly eliminated all potential challengers. Victor gives Rain a choice: kill a government minister or die a grisly death. But the best route to the minister is through his gorgeous Italian wife, Maria, a route that puts Rain on a collision course not only with Victor but with the shadowy forces behind the Russian's rise to dominance -- and the longings of Rain's own conflicted heart.

It's a battle between kingpin and newcomer, master and apprentice, a zero-sum contest that can only end with one man dead and the other the world's foremost assassin.