The Fire Pony (paperback) Rodman Philbrick
Joe Dilly has a secret way with horses- and with fire. His kid brother, Roy, knows about both secrets, but he's not telling. Not when he and Joe hire on at the Bar None,a ranch that has a few secrets of its own. Because at the ranch Roy finds a wild pony that can run like the desert wind, and if he can break that pony, he can keep her.
But the past is beginning to catch up, and as terrible things happen at the Bar None, Roy must face the truth- the truith about Joe Dilly and the secret of the fire pony.