In their magic treehouse, Jack and Annie are again transported to King Arthur's realm, where invisible beings, giant ravens, and mistaken magic spells have a duke's castle in an uproar on Halloween night.

Magically transported to southwest China to find the final object needed to break the spell on the wizard Merlin's beloved penguin, Jack and Annie take a side trip to the world's largest giant panda reserve.

"'Please come to Camelot.' When they read this note, Jack and Annie know they must travel to Camelot and the castle of King Arthur. The magic tree house whisks them through time and space, where they find that the castle itself has been attacked and King Arthur himself has been gravely wounded. To save the kingdom -- and the king -- Jack and Annie must solve a riddle, trick a band of robbers, and journey to the worlds of myth to find a missing dragon....