What is the theme in Last Sacrifice: A Vampire Academy Novel by Richelle Mead?

Friendship is a theme in this book. Rose and Lissa are best friends. Adrian and Eddie are very close friends of Lissa's as well. The bind of friendship between Lissa and Rose is real and a spiritual one. Spiritually, Rose can link into Lissa's mind to see what Lissa sees and feel what Lissa feels. When Rose is charged with the murder of the queen, Lissa and her friends plot to break Rose out of prison and buy some time while they investigate to find the real killer of the queen. An unlikely friendship also forms between Rose, Dimitri and Sydney. Alchemists do not tend to take the sides of vampires, but Sydney believes that Rose is innocent, so she puts herself on the line to help Rose.