Nancy, Bess, and George can hardly believe their eyes when they arrive at the Black Hills Buffalo Ranch. Aside from the awesome natural scenery, Mount Rushmore National Memorialwith four larger-than-life US presidentstowers nearby. But the girls have no time for sightseeing: Theyve come to help Besss friend Kincaid Turner find out who stole a baby buffalo named Justice from her fathers ranch. At first, stealing a buffalo seems like a strange thing to do, but as Nancy and her friends investigate, they find a whole herd of suspects. Antoinette Francoeur, an eccentric animal rights activist, makes a habit of freeing caged creatures. Badger Brady, a rival buffalo rancher, has been making threatswith an ax. And some archaeologists in the area arent happy about the girls snooping. Now its Nancys turn to round up the clues and stop a buffalo thief in his tracks.