When young Tuk is born on the mountain, life is simple for a young bighorn. Run, jump and play with his bandmates, eat and grow strong. But soon it will be up to Tuk to lead the herd to a new mountain he has seen far to the west. It will be a long journey filled with dangers. Wolf, bear, wolverine, puma — and man.

The responsibility to lead the herd sits uneasily on Tuk's shoulders. But Tuk is the one who has seen the blue mountain in the distance, and his bandmates are counting on him. There is little Mouf, full of questions. There is Sham, who must reach their new lambing grounds before her lamb is born. And there are his male rivals, who challenge his ability to lead them. After all, Tuk is just a yearling, and his horns are not even fully formed.

As the journey lengthens, it becomes more urgent. Swamps and impenetrable forests block their path. Hungry predators demand their due. Human highways and machines and dwellings contaminate formerly pristine valleys.

Yet Tuk finds a way, with the help of his friend Rim, the loyal ewe, Dall, and his trust in Blue Mountain — a place where the bighorn can live in peace, on the gifts that the mountain provides.