Pretty Girl Thirteen by Liz Coley

Angie Chapman is walking to the front door of her house.  Which is a little odd because the last thing she remembers is being in the woods at Guide Camp and the sight of a strangers eyes.  There is a plastic bag in her hand and she is wearing clothes she would never choose.  A strange ring on her finger, fingers that look odd, and scars on her wrists.  As she unlocks her front door to let herself in and calls out her mother hurtles hysterically down the stairs to meet her.  And Angie's nightmare begins.  She isn't 13 any more, she's 16 and the past 3 years have been simply lost to her.

Angie faces the trauma of medical examinations, police questioning and finally returning to high school and the friends who are 3 years older than she remembers them.  Psychiatrist Dr Grant is employed to help with Angie's amnesia and it emerges that she is suffering dissociative identity disorder: her self has fractured into separate personalities who developed to protect Angie from her ordeal but are not yet ready to communicate with her.

An absolutely gripping thriller that had me telling my family to go away so I could finish it and I was sad to finish it, really the highest praise I could give a book.