The #1 bestselling chapter book series of all time celebrates 25 years with new covers and a new, easy-to-use numbering system! Cannon fire! That's what Jack and Annie hear when the Magic Tree House whisks them back to the time of the American Civil War. There they meet a famous nurse named Clara Barton and do their best to help wounded soldiers. It is their hardest journey in time yet—and the one that will make the most difference to their own lives!