Kill You Twice by Chelsea Cain
Archie Sheridan should be healing – mentally and physically – from his past run-ins with serial killer Gretchen Lowell. But while he seems to be making some progress, he’s just as haunted as the day she let him go. He tries to focus on his work: a cyclist has come across a corpse in Mount Tabor Park on the eastern side of Portland. The man was gagged and hanging by his wrists from a tree, his torso skinned. It is the brutal work of a killer bold enough to torture his victim for hours on a sunny summer morning in a big public park.
The investigation isn’t far along before Archie gets a call from an unlikely source. In fact, after months of ignoring calls from a doctor at the mental hospital where Gretchen is supposed to be locked away forever, Archie is surprised to hear that she claims to have inside knowledge about the new investigation, and finally agrees to see her face-to-face. Archie is sure she is bluffing just to get close to him, but he can’t take the chance of losing his only lead.