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. Kathleen and Teddy are two apprentices who befriend Jack and Annie during their adventures, with one of these adventures being to free Teddy from a spell. The two occasionally join Jack and Annie, and, when they don’t, provide them support instead. During Super Edition #1, Teddy sends them on a mission instead of Morgan or Merlin. The companion “Magic Tree House Fact Trackers” are co-written by Mary Pope Osborne with her husband Will Osborne or her sister Natalie Pope Boyce.