When the Beast Ravens — E. Rose Sabin

The thrilling conclusion to the award-winning fantasy trilogy that began with A School for Sorcery...
As Gray Becq is about to discover, there are fates worse than death. It has been a full year since his escape from the Dire Realm. A year since a fellow student--having used his powers of sorcery to league himself with dark forces--betrayed him. Locked him away in a world beyond time, a world of unspeakable evil and unbearable tortures. Had it not been for Tria Tesserell and her extraordinary powers, he surely would have died. Now he almost wishes he had.
For no sooner has Becq adjusted himself to the familiar surroundings of The Lesley Simonton School for the Magically Gifted than a series of horrible accidents occur. Suspicion falls on Gray. Could he have brought a demon back with him from the Dire Realm? To find the truth, Gray will have to confront the most powerful demon he has ever faced: the demon that lies within.