George and Harold are forced to contemplate a world without Captain Underpants.

Jack and his younger sister take a trip in their tree house back to ancient Egypt, where they help a queen's mummy continue her voyage to the Next Life.

Their magic tree house takes Jack and Annie back to a monastery in medieval Ireland, where they try to retrieve a lost book while being menaced by Viking raiders.

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.

Eight-year-old Jack and his younger sister Annie find a magic treehouse, which whisks them back to an ancient time zone where they see live dinosaurs.

Their magic tree house takes Jack and Annie deep into the sea, where they meet up with dolphins, sharks, and octopi as they search for the answer to an ancient riddle. Morgan le Fay will make Jack and Annie masters of the tree house if only they can solve four riddles -- which will take four books, of course! Dolphins at Daybreak begins the third set of four books in this magical (and increasingly popular) series! Jack and Annie are off in the Magic...

"When Callie finds herself in the Antarctic, she's thrilled to meet a colony of Adélie penguins, ready to march north for the winter! But then a blizzard blows in, separating a baby penguin and her injured mother from the group" -- Page [4] cover.

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.