The First Rule — Robert Crais

When suburbanite Frank Meyer and his family are executed during a home invasion, the police begin investigating the secret life they're sure Meyer had. Joe Pike is on a hunt of his own: to clear his old friend's name, and to punish the people who murdered him. What starts out a simple trail gets twisted fast by old grudges, double crosses, blood vengeance, and a crime so terrible even Pike and his partner, Elvis Cole, have no way to measure it.