The safe house - Nicci French

A compulsively readable, highly sophisticated
psychological thriller from the author of THE MEMORY GAME.
There has been a savage, murderous attack on a house in the quiet prosperous suburb of a provincial English town. It has left two dead, and a teenage girl with her throat cut but alive.
In search of a haven for their one witness, the police turn to Dr Samantha Laschen, a specialist in post-traumatic stress. But what begins as a favour and a professional experiment ends as a fight for her sanity, for the truth, and ultimately for the very survival of all that is most precious to her.