Hades by Candice Fox

Fox’s first novel is dark and probing.  Hades is a man who fixes things for criminals.  But when he’s brought a car with two battered and wounded children inside, he cannot dispose of them.  Instead he takes them in and raises them.  But Eden and Ethan can’t forget what happened to them and who the men were who killed their parents.  When they grow-up, they’re brilliant, they become cops, then detectives in the police department, and they’re sociopaths when it comes to their enemies.  And they’ve been using their resources to hunt down and kill the men who killed their parents.  There’s only one left.  Enter our narrator, the new partner to Eden.  The last one died in action.  Our narrator has his own problems, with alcohol and with women.  He becomes suspicious of the brother and sister detectives, but he’s busy dealing with a surviving victim of a serial killer.  The ending is both inevitable and a surprise.