In the third book of the American history cluster, Jack and Annie are whisked to a midwestern prairie in the 1870s. They visit a one-room schoolhouse and learn about the hard life of the pioneers. When they return to the magic tree house, Jack and Annie spot a twister on the horizon. Is there time to warn the teacher and the children back at the schoolhouse? Or should Jack and Annie just save themselves? Amazon.com In book 23 of the Magic Tree House, award-winning author Mary Pope Osborne's popular young adventure series, siblings Jack and Annie travel back to American pioneer times. Their task, assigned by mysterious Camelot librarian Morgan le Fay, is to find "something to learn." When their magic tree house alights on a Kansas prairie in the 1870s, Jack and Annie quickly find a one-room schoolhouse with classes in session. Something to learn! After an all-too-brief school day, the two return to the tree house with their mission completed. But wait: "In the distance, twisting black clouds had dropped out of the storm clouds. They swirled into a funnel shape." A twister! And the young teacher and students in the school don't realize there's a storm cellar under the floor. Jack and Annie must brave the howling winds to return and save their new friends.