The Last Temptation by Val McDermid

Coming to terms over her breakup with criminal profiler Dr. Tony Hill, Chief Inspector Carol Jordan plunges into a risky undercover sting: track down a European drug trafficker and gain his confidence. But she's being tracked as well-by a serial killer whose psychosexual madness is born out of the darkest corners of history. In quiet isolation, Tony Hill is laying to rest the scars of his past-until he's recruited back into business on a case he can't ignore. An evil is striking uncomfortably close to home, and casting a killer shadow over the life of his long-time colleague and sometimes lover. As the danger closes in, and as Tony and Carol cross paths to navigate the terrain of a shattered human mind, they have no one left to trust but themselves-and fear that there's no place left to run as a killer promises to fulfill his most twisted dreams.