Fortress of the Stone Dragon: A Branches Book (Dragon Masters #17)

Not All Of The Wizards Who Were Freed From Maldred's Time-trap Were Good Wizards; One Of Them, Astrid, Is Planning On Working A Spell That Will Bring To Life The Bones That Lie Scattered In The Fortress Of The Stone Dragon, Bones That Belonged To Creatures Much Bigger Than Dragons--and When His Friends Are Turned To Stone It Is Up To Drake To Find A Way To Save Them, Including His Own Dragon, Worm.