EQUUS centres on the explosive encounters between seventeen-year-old Alan Strang, who has blinded six horses with a spike, and Martin Dysart, the child psychiatrist who agrees to treat him.

Peter Shaffer based the plot on an allegedly true story. The play is structured like a mystery, as Dysart struggles to determine what drove Alan to commit the crime. But Equus is far from a conventional mystery, in which solving the crime relieves tension and restores a stable society. Instead, Dysart's search for the meaning of Alan's act leads him to doubt his own vocation and integrity. The closer he comes to understanding his patient's motives, the more confused Dysart is about how he should respond to Alan and the mental world he has created.

Peter Shaffer wrote three major stage plays in the 1970s: The Battle of Shrivings (1970), Equus (1973), and Amadeus (1979). After premiering in 1973 in London, Equus ran for more than a thousand performances on Broadway and won the Tony Award, the New York Drama Critics Awards for best play as well as three other major drama awards. The play took critics and public alike by storm and has gone on to become a modern classic.