In the 1970s, American director Sidney Lumet was preoccupied with one particular type of character: men on the verge of breakdown. Whether it was Sean Connery’s dangerously curious detective in The Offence (1973), Al Pacino’s robber in crisis in Dog Day Afternoon (1975) or Peter Finch’s neurotic news presenter in Network (1976), he was drawn to men teetering on the cusp of madness.

In Peter Shaffer’s 1973 play, Equus, Lumet found another fragile set of male minds ready to be picked apart. In collaboration with Shaffer, he adapted it for the screen for release in 1977. Adding to his growing list of male neurotics were two of the most powerful roles in any Lumet film, portrayed by Richard Burton and Peter Firth. For Burton, the project proved a late-career high, giving him one of his last leading roles.

In both film and play, Equus follows the treatment of a patient called Alan (Firth) at a psychology institution. He’s been brought to the clinic of Dr Martin Dysart (Burton) after being arrested for blinding the eyes of several horses in a fit of psychosis at the stable where he worked.

Soon, Dysart is fitting together the pieces of Alan’s fractured psychology, from his complex upbringing by his devout mother (Joan Plowright) and tough father (Colin Blakely) to his early childhood experiences and, finally, his confused desire for Jill (Jenny Agutter), the daughter of the stable’s owner, Harry (Harry Andrews).

Dysart begins to comprehend the complex troubles haunting Alan. But, in understanding them a little too deeply, Dysart may have destabilised his own world view, one that looks on in quiet envy at Alan’s tormented but pure devotion to the psychosexual God his mind has conjured from the patchwork of modern life.

Few films deal quite as explicitly with the horrors that fill the moral hollow left by the death of God. Lumet stays true to the discomfort and tough questions asked in Shaffer’s powerful play. Religious mantras are replaced by parroting slogans from adverts, while repressed sexuality spawns a new equine God. Equus is a psychodrama of sorts, but also a gothic film. Its ritualistic, phantasmagorical qualities highlight a very particular twisting of theology into something demented and unique.

Equus (1977)

Simply on a visual level, its grim domestic horrors share something of the grimy hopelessness of films like Richard Fleischer’s 10 Rillington Place (1971) or Lumet’s equally dank but brilliant The Offence. Even with these qualities, however, the true power of the film comes from its lead performance by Richard Burton.

Equus is structured in flashback, with Dysart seemingly breaking the fourth wall for long portions of the film. It’s difficult to imagine another performer carrying such heavy material in the same way, Burton’s stare and drawl stitching together the narrative of how Alan first descended into this dark search for passion, in the most theological sense of the word.

In this way Lumet makes the most of the play’s strengths. The film is essentially conversational, though those conversations are tense to the point of mania and prove deeply cinematic.

Equus (1977)

Equus is also interesting from the perspective of Burton’s career. By this point, he was increasingly finding himself in below-par films, leading up to Equus with the likes of Terence Young’s The Klansman (1974) and John Boorman’s atrocious Exorcist sequel, Exorcist II: The Heretic (1977). Lumet’s film was a return to material worthy of his talents.

Such were the actor’s health issues during shooting that his filming was completed in haste. All of his monologues given to camera – some of the best screen moments in his career – were filmed across one day due to the actor’s back pain. His torment at times seems genuine. The discomfort he was in is channelled into something almost vitriolic. Certainly, he’s believably a broken man.

It was a role Burton clearly understood. He’d replaced Anthony Perkins in the stage play during its Broadway run in 1976, and had hoped that the screen version would give his career a new lease of life.

His hopes were partially fulfilled when his biting turn earned him another Oscar nomination. This was Richard Dreyfuss’s year though, and Burton wouldn’t be nominated again. In fact, the film flopped despite its critical success, and Burton seemed relegated again to enjoyable but schlocky genre roles, such as in Andrew V. McLaglen’s war thriller The Wild Geese (1978) and Jack Gold’s underrated The Medusa Touch (1978).

Major performances in Tony Palmer’s miniseries Wagner (1983) and Michael Radford’s Orwell adaptation Nineteen Eighty-Four (1984) were to come before his death, yet Equus stands as a late highlight in the actor’s long and illustrious career. Few such autumnal pinnacles have been as fittingly detailed or troubling, reflecting the skill and complexities of a truly great leading man.