At the outset of this novel, the intrepid Jack and Annie are invited to come to Camelot for Christmas Eve. Without a research book for the first time ever, the two kids set off in the Magic Tree House. No sooner do they arrive at the castle, when a dark knight appears and freezes King Arthur and all his court- including Jack and Annie’s friend Morgan le Fay. Jack and Annie set off to the Otherworld to find the Cauldron of Poetry and imagination, which is the only thing that can save Camelot.