In this latest installment of the magical series, Jack and Annie are whisked off to the vast plains of Africa, where they must solve Morgan le Fay's third magical riddle. Once the riddle is solved, they still have to get past a pride of lions, a herd of rampaging wildebeests, and one very hungry Masai warrior. Magic Tree House is a book series for young children by Mary Pope Osborne. The series features two children, the bookworm Jack and his adventurous and imaginative younger sister Annie, who travel to historical places using a magic tree house. The magic tree house belongs to Morgan Le Fay who, in the series, is King Arthur's sister and a librarian. She uses the magic tree house to gather books from time and space. Jack and Annie travel by opening a book, pointing at a picture of a place and then wishing that they could go there.