Between Worlds by P.J. Roscoe
When a young woman who has been missing for months turns up battered and bloodied, lying next to a headless corpse, the police are convinced that she is the killer – but why? The only clue is the murder weapon, an ancient sword dating from the 6th century, that has police and historians baffled. Refusing to talk, Emily is sent to a psychiatric hospital for her own safety. Dr. Marian Griffiths is determined to get ahead in her career, and sees Emily as a way of doing that. Using hypnotherapy, she finally has a breakthrough and Emily begins to talk;…