Nightfall — L.J. Smith

To save the two vampire brothers who love her, Elena Gilbert sacrificed her life.

Now that a supernatural force has brought Elena back from the dead, all handsome, brooding Stefan wants is to keep her safe. But when he is lured away from Fell's Church, sleek, powerful Damon seizes his chance to win Elena over, unaware of the danger they're both in. A malevolent being has infiltrated the town and is growing stronger. Able to possess Damon at will, the creature is also drawn to Elena and the new power she has acquired. But it's after more than Elena's power: It thirsts for her death.