After the violent blinding of six horses with a metal spike in a stable, a psychiatrist is called in to examine the unassuming young boy responsible, but is also forced to confront his own demons in the process.
On stage, Peter Shaffer's play Equus can have as powerful an impact as his Amadeus. It loses something in this screen translation, however, precisely because it is too reverential towards the theatrical text.
Even Richard Burton, talking straight to camera, can't bring a properly cinematic dimension to the monologues, while his scenes with Peter Firth the young patient his psychiatrist is treating after a horse-blinding incident are hemmed in and theatrically stylised.
The mix of repressed sexual desire and religion at the root of the boy's problems feels a little clichéd today; but when Shaffer's writing hits its peaks, his genius shines through Sidney Lumet's unadventurous staging.
It's not as gleefully cinematic as the big-screen adaptation of Amadeus, but the sheer power of the writing means that it is still worth a look.