The Color of Bone. Wren Delacroix, #5

When Wren Delacroix and Detective Caius Reilly investigate a new crime scene, they're surprised to discover the killer has left a personal note, addressed directly to Reilly. As they unravel its cryptic message, they are led down a twisty road to reveal secrets about Reilly's past and about his mother, a victim of the serial killer Mark Quentin Rhoads. This new killer means business. He's vicious.
He's smart. He's brutal. He's playing a game with them. But only he knows the rules.