HYSTERIA by Megan Miranda

Mallory killed her boyfriend, Brian. She can't remember the details of that night but everyone knows it was self-defense, so she isn't charged. But Mallory still feels Brian's presence in her life. Is it all in her head? Or is it something more? In desperate need of a fresh start, Mallory is sent to Monroe, a fancy prep school where no one knows her... or anything about her past. Then, one of her new classmates turns up dead. As suspicion falls on Mallory, she must find a way to remember the details of both deadly nights so she can prove her innocence--to herself and others.