Heartsick by Chelsea Cain

Damaged Portland detective Archie Sheridan spent ten years tracking Gretchen Lowell, a beautiful serial killer, but in the end she was the one who caught him. Two years ago, Gretchen kidnapped Archie and tortured him for ten days, but instead of killing him, she mysteriously decided to let him go. She turned herself in, and now Gretchen has been locked away for the rest of her life, while Archie is in a prison of another kind---addicted to pain pills, unable to return to his old life, powerless to get those ten horrific days off his mind. Archie's a different person, his estranged wife says, and he knows she's right. He continues to visit Gretchen in prison once a week, saying that only he can get her to confess as to the whereabouts of more of her victims, but even he knows the truth---he can't stay away.

When another killer begins snatching teenage girls off the streets of Portland, Archie has to pull himself together enough to lead the new task force investigating the murders. A hungry young newspaper reporter, Susan Ward, begins profiling Archie and the investigation, which sparks a deadly game between Archie, Susan, the new killer, and even Gretchen. They need to catch a killer, and maybe somehow then Archie can free himself from Gretchen, once and for all. Either way, Heartsick makes for one of the most extraordinary suspense debuts in recent memory.