Last Sacrifice by Richelle Mead

Framed for the murder of Queen Tatiana, Rose Hathaway finds herself imprisoned while her best friend, Lissa Dragomir, struggles to prove her innocence amid royal court chaos surrounding the queen's funeral. As Rose navigates confinement and impending trial, allies work from the outside, uncovering secrets and conspiracies that suggest Rose was set up. Unexpected escapes, dangerous confrontations with enemies both living and undead, and the revelation of a long-lost Dragomir relative further complicate their efforts. Ultimately, they strive to expose the true killer and secure Lissa's place in a changing Moroi world, while Rose grapples with her feelings for her former lover, Dimitri, and her current relationship with Adrian.