The Edge of Normal by Carla Norton

Second Hand 

Tell me, what are you really afraid of . . . ? Reeve St Claire was abducted when she was twelve years old and held in captivity for four years. Now, in her twenties, she has a fragile stability but with the help of her psychiatrist, she has started to build a life of independence. But she will never shake off the terror and memory of the monster she believes is behind bars. When Tilly Cavanaugh is rescued from a basement having suffered a similar experience, her parents call Reeve to ask for her help in helping their daughter rediscover a ‘normal’ life. But it is only when two other girls go missing that the police confirm the link and that there is a serial abductor in their midst. Reeve knows that she alone has the knowledge which will help to find the perpetrator - but can she overcome her demons to discover the truth?