Spirit Bound by Richelle Mead

Spirit Bound is the fifth book in the Vampire Academy series by Richelle Mead.
After a long and heartbreaking journey to Dimitri's birthplace in Siberia, Rose Hathaway has finally returned to St. Vladimir's and to her best friend, Lissa. It is nearly graduation, and the girls can't wait for their real lives beyond the Academy's iron gates to begin. But Rose's heart still aches for Dimitri, and she knows he's out there, somewhere. However, she has to first focus on passing her trials to become a guardian and hope it will be enough for her to get assigned to Lissa. Then she can work on a plan to save Dimitri, even though her information may be based on a lie and the plan may endanger her life and Lissa's. Spirit Bound's release pushed the Vampire Academy series into the #1 slot on the New York Times list for children's series. The book Spirit Bound begins with Rose taking her guardian trials, enabling her to leave St. Vladimir's Academy as a qualified guardian. After passing her trials with flying colors and receiving her promise mark, Rose - along with Lissa, Christian, Adrian, Eddie and the other dhampir graduates - head to the Royal Court to begin life outside of the academy. Rose and Adrian are currently attempting a relationship after she promised him she would give him a shot after she got back from Russia in Blood Promise. However, after learning that there is a way Dimitri can be saved from being a Strigoi, Rose sets off on a mission with Lissa to break Victor Dashkov out from prison when she learns that only he can help them to find out how to turn Dimitri back into a Dhampir. (Summary by Wikipedia)