Their magic tree house takes Jack and Annie back to the Wild West, where they experience excitement and danger and try to solve a riddle. Jack and Annie are on a mission to solve a riddle. They journey back to the Wild West in their time travelling tree house. They encounter rattlesnakes, horse thieves, a lost pony, and a ghost among other things. They have to tie together all of their experiences in and around this ghost town to complete the riddle. Osborne creates a fun and occasionally suspenseful story line. The uncomplicated text and easy to follow plot make this a valuable introduction to chapter books for beginning readers. It is part of the "Magic Tree House" series, and several references made to previous books in the series.