Martin Dysart, a child psychiatrist, recognizes that his life is filled with emptiness and pain. He is confronted by this recognition through his treatment of Alan Strang, an adolescent who inexplicably blinds six horses with a horsepick. It is a crime that shocks and outrages the owner of the stables, who believes that Alan should be imprisoned. However, Hesther Salomon, the magistrate in charge of the case, recognizes a deep need in the boy, and she brings him to Dysart hoping that he can make the boy “normal.” Dysart comes to recognize that he can, but at a terrible cost.

At first distrustful of Dysart, Alan sings jingles to block Dysart’s overtures. Unperturbed, Dysart begins seeing Alan and then begins to make inquiries. He finds the Strang household to be absolutely normal superficially, but, beneath this appearance of normality, strange tensions vibrate. Mr. Strang is dictatorial and repressed; Mrs. Strang is filled with religious mania. Neither is able to deal in any real way with what happened.

Alan himself seems unable to deal with his actions, and Dysart works to find ways to allow Alan to tell him things that will help to explain the blinding of the horses. Using a small recorder, Alan tells Dysart of his first encounter with a horse on a beach when he was six years old. A rider took him up and down through the surf, Alan glorying in the ride until his enraged father pulled him down from the horse, claiming that the horse and rider were menaces to safety. For Alan, it was a moment of great passion; it began his sense of a godlike spirit in horses, a god he named Equus.

From Mr. Dalton, Dysart learns that Alan was introduced to the stable by Jill Mason, and at first he believed that he found a good worker, since Alan did much more than his share of grooming the horses and cleaning the stables. Oddly, however, Alan never rode the horses, though Mr. Dalton suspected that periodically they were ridden at night. Clearly, Alan was passionately fascinated by horses; in fact, he worshiped the god Equus in them, something Mr. Strang discovered disconcertingly when he saw Alan chanting before a picture of a horse, putting a bit in his own mouth, and beating himself.

Dysart is more and more taken with Alan; he sees in him someone who is filled with a passion, whose life is filled with worship, and he envies Alan. His own life seems so safe and secure, so empty of energy and passion that he questions whether his treatment of Alan is anything less than a monstrous sacrifice to the normal.

Under hypnosis, Dysart takes Alan’s mind back to one of the nights when he took a horse, Nugget, out riding. It was an evening of passionate devotion, of the worship of the god Equus. Alan led the horse gently out from the stables to a field, where he stripped and bowed to the god. He inserted a bit in his own mouth, and then, in complete worshipful ecstasy, he galloped around the field. Afterward, he stood beside the horse, fully devoted, fully alive. It was a sense of passion that Dysart never experienced.

Soon after, Mrs. Strang comes to visit Alan, and, in a terrible fight, he silently accuses her of some responsibility for his behavior. She refuses to accept the accusation, and, when Dysart intervenes, she claims that what Alan did is Alan’s responsibility, not that of his parents. Nevertheless, she also blames the Devil and leaves without any real understanding of what is troubling...