Young Cassie Louise Lightfoot, who soared above New York City rooftops in the Caldecott Honor Book (and Coretta Scott King Award-winning) Tar Beach, returns for an imaginative historical adventure. Cassie and her brother, Be Be, are on another fanciful flight when they encounter a mysterious train and a woman in a conductor's uniform: Harriet Tubman, known as "Aunt Harriet" because she takes care of people. Tubman sends the two children on separate re-creations of a journey from slavery to freedom. As Cassie makes her way north, she relies on Tubman's advice to stay safe, and takes comfort in notes from Be Be, who is always one step ahead. The children are reunited in Canada, where they can celebrate the freedom they have always known with newly open eyes. As Be Be says, "Now I know what our great-great-grandparents survived when they were children." In her unique artwork, which fans will recognize from Tar Beach and from the many "story quilts" that have brought her international recognition, Faith Ringgold uses strong colors and shapes to merge fact and fancy and bring out the excitement inherent in this historical adventure. A map and short bibliography are appended, as well as an author's note giving more information on Harriet Tubman and the Underground Railroad, and on the creation of the book. A useful introduction for the picture-book set, Aunt Harriet's Underground Railroad in the Sky will engage readers to understand this important part of American history.