The Night Of No Tomorrow

Dungeon Master sends the children northward to the town of Helix to attend a local dragon-banishment celebration. On the way they meet Merlin in his magnificent sky castle. The wizard offers to make Presto his apprentice, only if the young mage chooses to leave his friends and stay there for the rest of his life. But is Merlin's once-in-a-lifetime offer all that it appears?