Morgan Le Fey, a magical librarian from the time of King Arthur, has charged a brave young pair of children with the task of freeing an enchanted dog from a spell by collecting four gifts. In the 18th easy-to-read chapter book in Mary Pope Osborne's Magic Tree House series, eight-year-old Jack and seven-year-old Annie travel back almost 200 years to the Great Plains to find a "gift from the prairie blue." Along the way, Annie and Jack make friends with young Black Hawk, narrowly miss a buffalo stampede, and learn about how the Lakotas view the earth and their place in it.