Vampire Academy. Book 4. Blood Promises

Strigois deal blow after blow to the Academy mercilessly. The latest attack has become the bloodiest in the history of the school, claiming the lives of many students and teachers. But the most terrifying thing is – the strigois took prisoners with them. And among them is Dimitri, the person most dear to Rose.
Tormented by the pain of loss, Rose sets off on a distant journey to find her beloved and take revenge on the dark creatures that kidnapped him...

The fourth book of the cult cycle by Richelle Mead in a convenient classic pocket format.