The Magic Tree House is an American series of children's books written by American author Mary Pope Osborne. The series consists of two groups. The first group consists of books 1-28, in which Morgan Le Fay sends Jack and Annie Smith, two normal children who are siblings from the fictional small town of Frog Creek, Pennsylvania, on numerous adventures and missions with a magical tree house. The second group, referred to as the Magic Tree House "Merlin Missions," begins with book 29, Christmas in Camelot. In the Merlin Missions, Jack and Annie are given quests by the ancient wizard Merlin the Magician. These books are longer than the previous 28, and some take place in fantasy realms like Camelot.