Peter Dunstan is a big rancher who wants to become bigger, to control more land. So when he buys Dr. Henry Morgan's ranchland that has been unsuccessfully converted to farming, it is his intention to return it to open range. The only stipulation the doctor makes is that Dunstan must retain Sandy Sweyn, who has more or less been Dr. Morgan's ward. Though the man is of age, he is generally considered a half-wit, even by the doctor. Still, Sandy has a fabulous gift: he can communicate with animals. The most refractory and savage bronco will yield to his subtly persuasive methods even when expert horse breakers have failed.

After Sandy gentles the totally recalcitrant gelding that Dunstan has been trying to break to the reins, he claims that his mare, Cleo, though used only for drudgery, could easily outrun the gelding in a race. Dunstan is so contemptuous of this boast that he bets $5,000 and ownership of the gelding if he loses the race. As it turns out, Cleo readily wins.

Rather than indulging his anger, Dunstan decides to use Sandy's gifts to his advantage by getting him seemingly impossible tasks. The problem is that after each of these incredible tasks is accomplished, some personal misfortune befalls Dunstan. Finally Dunstan drives Sandy into the mountain wilderness, where his prowess eventually becomes legendary. But banishment is no solution for Dunstan when he comes to need Sandy more than ever, and his only way of getting him back is to resort to trickery.