A psychiatrist, Martin Dysart, investigates the savage blinding of six horses with a metal spike in a stable in Hampshire, England. The atrocity was committed by an unassuming seventeen-year-old stable boy named Alan Strang, the only son of an opinionated but inwardly-timid father and a genteel, religious mother. As Dysart exposes the truths behind the boy's demons, he finds himself face-to-face with his own.

Through his characters, Shaffer explores the dilemmas of late-twentieth-century existence in England and, by extension, in the entire industrialized world. In an increasingly commercial and mechanized culture, there is little place for ecstasy and worship, yet they remain human endowments. Is our trust in science as foolish—even more foolish—than the pagans' belief in their gods? Does being "normal" in such a culture also entail losing one's individuality and learning to live without passion?

After premiering in 1973 in London, Equus ran for more than a thousand performances on Broadway and won the 1974 Tony Award, as well as three other major drama awards.