Andy and Terry are trying hard to write their next book but they are constantly distracted by the many animals and special rooms in their thirteen story treehouse.
Eight-year-old Jack and his seven-year-old sister, Annie, learn about the ocean, solve the mystery of its fabled sea monster, and gain compassion for their fellow creatures after joining a group of nineteenth-century explorers aboard the H.M.S. "Challenger.".
On Christmas Eve, Jack and Annie's tree house transports them to King Arthur's castle at Camelot, where they undertake a quest to the castle of the Otherworld.
Jack and Annie continue to try helping Merlin the magician by searching for the secrets of happiness, and their magic tree house takes them to Antarctica, a wasteland where the penguins may know what to do.
Eight-year-old Jack, his seven-year-old sister, Annie, and Peanut the mouse ride in a tree house to the Amazon rain forests, where they encounter giant ants, flesh-eating piranhas, hungry crocodiles, and wild jaguars.
