Shadow’s Edge by Brent Weeks

Kylar Stern has rejected the assassin’s life. The Godking’s successful coup has left Kylar’s master, Durzo, and his best friend, Logan, dead. He is starting over: new city, new friends, and new profession.

But when he learns that Logan might actually be alive and in hiding, Kylar is faced with an agonizing choice: will he give up the way of shadows forever and live in peace with his new family, or will he risk everything by taking on the ultimate hit?