The body counter
(Book)

"Months after discovering the mastermind behind her own kidnapping, Detective Jude Fontaine is dealing with the past the only way she knows how: by returning to every dark corner of it. But it's a new, escalating series of mass slayings that has become her latest obsession at Homicide. At first, Jude and her partner, Detective Uriah Ashby, can see no pattern to the seemingly random methods, the crime scenes, or the victims--until they're approached by a brilliantly compulsive math professor. He believes that the madman's next move is not incalculable; in fact, it's all part of a sequential and ingenious numerical riddle. His theory is adding up. The body count is rising. But when the latest victim is found in Jude's apartment, the puzzle comes with a personal twist that's going to test the breaking point of her already-fragile state of mind. For all she knows, her number may be up."--,(source of summary not specified)