Grave Doubts by Elizabeth Corley
'He was only a pupil, learning from a master who was uncompromising about the rules of the game he had invented. Normally he obeyed them, but with her the temptation had been too strong. Otherwise he was an adept pupil, becoming more skilled every time. This one would be his best, he was certain. Perhaps tonight he might...even...kill her.' Having survived a terrifying attack as part of an investigation, Sergeant Louise Nightingale retreats to her remote family cottage to lick her wounds, comforted in the knowledge that her attacker is behind bars. But when a serial killer starts terrorising the country, her colleague, DCI Andrew Fenwick, questions whether or not they have the right man. For Nightingale, the true nightmare has only just begun...Spine-tingling suspense with a dark underbelly of psychological terror - this is a book you will not dare put down.