The Invisible Girl in Room Thirteen by Stephen Simpson is a young adult horror novel. 

The story follows Alison Locke, a girl who feels overlooked by her mother and is sent to a mysterious boarding school.

To gain social acceptance, she accepts a supernatural initiation challenge involving a Ouija board in the supposedly haunted Room Thirteen.

The narrative takes a dark turn as the ghost of a former student named Lily appears to establish a psychological connection with Alison.

This haunting leads to a violent series of murders on campus, eventually revealing a tragic historical link between Alison's father and Lily.

The story culminates in a harrowing climax where Alison appears to succumb to dissociative identity disorder or possession.