The Light Horse. Light Horse, Dark Horse, #2

Four years ago, Soter the Light Horse, Son of the Great Horse, was born to two young mustangs, which fulfilled the first phase of the Prophecy of the Light Horse. Now, as a full-grown young stallion, Soter leaves His family's herd to begin His mission: break the Curse of Evil and defeat the Dark Horse. But first, Soter befriends seven young stallions and appoints them His apprentices, his very first followers.
He then visits the many mustang herds in Great Plains, speaking words of wisdom and healing others with miraculous power. But not everyone is convinced that Soter really is the Light Horse. As conflicts rise among the herds, Soter's friends are about to discover that there is more to the Prophecy than they even realized.