(Description nicked from B&N.com.)
“Spirit White and her friends Burke, Loch, and Addie have escaped from Oakhurst Academy. But their freedom has come at a terrible cost—a dear friend sacrificed her own life to save theirs. In the wake of Muirin’s death, they are also forced to deal with the terrifying truth behind the facade of Oakhurst Academy: all of the legends are true.
Queen Guinevere, King Arthur and the Knights of the Round Table really had existed. With the magic of Merlin, they were able to imprison their greatest foe, Mordred, before he could plunge the world back into the Dark Ages. But Mordred is now free, in charge of Oakhurst Academy, and determined to finish what he started so long ago.
Pursued by Shadow Knights, the reincarnated remnants of Mordred’s original army, Spirit’s small band undertakes a quest to recover the Four Hallows, objects of immeasurable power. Memories of a past life have begun to surface, one in which Spirit wields a legendary sword. She comes to realize that these memories are the true key to Mordred’s defeat. Can Spirit and her friends manage to recapture the magic of Camelot in time to save their fellow students and prevent the end of the world?”