The Blackbird's Song by Katie Marshall

After his mother’s death, Brian suffers severe trauma from his abusive father. When the abuse becomes too much, Brian’s mind splits into multiple personalities and starts him down a path of murder and destruction. Lizzie ’s life is turned upside down when she is tortured by a serial killer. Now she has to learn to cope with a new school, new friends, and a new life with a sister that she didn’t meet until recently. As Lizzie struggles to discover the identity of the man who ruined her life, people think she’s crazy and suffering from delusions. But when Lizzie finally discovers that Brian was her attacker, the two collide in a battle of survival…