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 travel in their magic tree house to the land of the mystical selkies to seek a magical sword for Merlin.

While on a mission to prove to Merlin that they can use magic wisely, Jack and Annie travel to seventeenth-century Venice, Italy, to save the city from disaster.

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

Blizzard of the Blue Moon
Jack and Annie are off on another Merlin Mission. This time, Merlin has sent them to rescue a beautiful magical creature–the unicorn. But when they land in New York City during the Depression of the 1930s, Jack and Annie are confused. Where will they find a unicorn in a big city? And what about the blizzard that's burying New York in snow? Can Jack and Annie make their way through the windy streets, find the...

Haunted Castle on Hallow's Eve
The castle looms dark against the light of the moon. Merlin the magician needs someone smart enough to solve the mystery of how the castle became haunted and return it to its rightful owners—so Jack and Annie take on their second Merlin mission in the magical realm of Camelot.

Summer of the Sea Serpent
Jack and Annie are off on another mythical mission at the request of Merlin...

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.