Killing You Softly — Lucy Carver

After the tragic events of last term, Alyssa arrives back at St Jude's to a school full of freaked-out students. They are wary of her ability to remember every tiny thing they do, and Alyssa's beginning to feel lonely and ostracized. Then she gets an email, seemingly from a secret admirer. He teases her about her photographic memory and challenges her to prove how good it really is. At first Alyssa is intrigued and likes showing off her talent, but as her admirer's challenges get darker and more extreme and there is a murder in the nearby town, she realizes she's in too deep. Now her memory might be the only thing that can help her understand the killer and save her from the same fate . . .