Riven

Augum, Bridget, and Leera want only to study new spells and make their legendary mentor proud. But when she unexpectedly departs on a crucial quest, they run afoul of a devious old witch and are forced to make a hasty getaway-straight into the hands of a notorious maniac known as the Blade of Sorrows. Prisoners of the Blade and his sadistic apprentice, the trio must face their greatest challenge yet: escape using nothing but an ancient spell with some nasty side effects. But more than their lives are at stake, for an entire kingdom's hopes rest with their mentor-and she's heading for a deadly trap.