Wild Blood (Horses of the Dawn, Bk. 3)

After adopting an orphan human boy, the First Herd is finally ready to make the treacherous journey across the mountains to find the Sweet Grass that promises survival. But when their leader, Estrella, is captured by cruel men, it delivers a blow to the very heart of the herd. If the horses turn back, they'll never make it across the mountains before winter. But if they leave Estrella in captivity, the wild-born filly will surely perish.