Vampire Diaries: The Return: Nightfall – L. J. Smith

Vampire Diaries: The Return: Nightfall is the third book (though the first two both contain two 'parts') in the series. It begins as Elena has come back from the dead – again. She's no longer a vampire, but she's also no longer human. Trouble is, nobody seems quite sure what she is. She's temporarily forgotten everything and Stefan has to look after her as though she were a child. Somehow, Stefan knows that she will soon regain her memory and become more like the old Elena.

Stefan's right...