Mary Pope Osborne

The magic tree house carries Jack and Annie to New York City in 1938 on a mission to rescue the last unicorn.

When Merlin is weighed down by sorrows, Jack and Annie travel back to feudal Japan to learn one of the four secrets of happiness.

Guided by a magic rhyme, Jack and Annie travel to ancient Baghdad on a mission to help the Caliph disseminate wisdom to the world.

Jack and Annie visit the Paris World's Fair of 1889 in an effort to protect four scientific pioneers from an evil sorcerer.

When eight-year-old Jack and his seven-year-old sister, Annie, join a group of nineteenth-century explorers aboard the H.M.S. Challenger, they learn about the ocean, solve the mystery of its fabled sea monster, and gain compassion for their fellow creatures.

Travel to Ancient Greece with Jack and Annie as they meet Alexander the Great and help tame his wild stallion.

Jack and Annie travel back to 19th-century Ireland to inspire a young Augusta Gregory to share her love of Irish legends and folktales with the world.

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.

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.

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.