Batgirl #21

The key to the case lies in Cass's mind! There has been a murder, and the only clues are buried deep in Batgirl's memories — along with the phrase “forget me not.”

Trapped in the prison of her past, Cassandra Cain must unmask the killer before it's too late. But as she lives her time with David Cain over and over again, the question is: will she solve the murder in time — or lose her mind entirely?