Mystery of the Missing Mustangs — Penny Warner

Four Courageous Scouts Search for the Missing Mustangs! The four fearless scouts from Troop 13 are back again for another wild adventure, this time at a dude ranch in the western plains of Nevada. While learning how to care for horses, thirteen-year-old Sierra and her three best friends CJ, Becca, and Jonnie learn about the mysterious disappearance of government-protected wild horses, one of which was supposed to be adopted by their new friend Devyn. When the four friends decide to help Devyn find her horse, they discover it won't be easy, not with a suspicious rodeo owner standing in the scouts' way and leading them to believe someone is stealing the horses and using them for illegal purposes.