This academic year has been bookended by two stonking productions of plays by Peter Shaffer. Back in Michaelmas Term there was Amadeus. And now there’s Equus, in a rendition so intense that it was only as the last spotlight flicked out on Ethan Bareham’s tortured face that the audience realised it hadn’t breathed for the last five minutes.

Amadeus and Equus are linked by more than just performance schedules. Equus may be the wordier and denser of the two. But both plays give free rein to Shaffer’s overriding preoccupation: the limitations of ‘normal’ people. Just as Salieri stands up as the ‘patron saint of mediocrity’, here Dr Dysart confesses to his own ‘educated, average head’. Both plays are narrated by characters who, despite achieving worldly success in their own fields, bewail the gulf between themselves and those who live in a world of pure, celestially-driven inspiration. Not only do they glimpse their own petty boundaries, but, in a kind of earthly purgatory, they are fated to be the only ones who truly understand and appreciate the genius of the outsider whom everyone else considers insane. In Amadeus it’s Mozart, and in Equus it’s the disturbed teenager Alan Strang. The play follows psychiatrist Dysart’s efforts to understand why Strang has blinded six horses with a metal spike.

Poor Peter Shaffer. It doesn’t take a genius to see where all this angst is coming from. His twin brother Anthony was of course also a playwright and screenwriter, responsible for such stone-cold classics as Sleuth and The Wicker Man. Peter was more prolific, but he may well have looked across the desk at those unhinged scripts of Anthony’s (especially The Wicker Man) and shrivelled up with envy. It all came out in his plays. And Marianne Nossair’s direction hones in on and releases all the paranoia trapped like shale gas in Shaffer’s script.

I don’t know if this is Nossair’s first outing as a director, but she is already well-established as a top-quality actor on Oxford stages (see reviews of Blindness, Bucket List, Window Seat and I Will Delete This Story). And Equus feels as though it has a real actors’ director at the helm. The performances are profound, controlled and understated, with flashes of mania and violence that both shock and fascinate. Nossair has confidence in her brilliant cast, and they repay it in spades. Secondary characters like Magistrate Hesther (Vita Hamilton), stable girl Jill (Chess Nightingale) and Alan’s father Frank (Ollie Gillam) are realistic and passionate, but at the same time intelligently subdued, allowing the two leads, Alan (Joe Rachman) and Dysart (Ethan Bareham) literally to take centre stage. This isn’t an assemblage of showy directorial concepts, but a sensitive understanding of how to balance a performance for maximum effect, like a well-designed house that gives due prominence to the main rooms. It would have been so easy to make Frank Strang an overbearingly boorish father, throwing his weight around and shouting others down, but Gillam’s unselfish, toned-down performance puts the emphasis where it needs to be.

As a result, the scenes between Dysart and Alan, which are the psychological meat of the play, crackle with nervous tension. Rachman is bewitching as Alan: a psychotic mixture of innocence and mistrust, repression and desperate desire to confess. The scene in which he re-enacts his midnight ride astride his horse-god is a triumph of physical theatre. Bareham, as his psychiatrist, somehow conveys the deserts of vast despair behind his life committed to pulling people back into a world deemed by society as normal. Bareham is a natural narrator: earlier this year he played Nick in The Great Gatsby, another character charged with drawing the audience into a bizarre world to which he is only a visitor himself. But in Equus he gets a chance to show the skull beneath the skin, and it’s a fitting climax to a student acting career.

The Shaffer theme that goes hand in hand with obsessive mediocrity is sexual repression, and fear of one’s own sexuality. Unlike his thrice-married, straight brother Anthony, Peter was gay, and was already in his mid-40s before homosexuality was legalised in the UK. In Equus, Alan’s terror at, and need to conceal, his sexual desires clearly echo that stigma. Nossair’s production unleashes the homoeroticism in the text with joyous indulgence. At one end of the scale, Alan’s religiously repressed mother (Grace Gordon) pours shame on her son’s head in a brilliant, mascara-running scene of supercharged emotion. At the other, Rachman nuzzles Nugget the horse’s (Ollie Perry Wade’s) neck in one of the play’s few moments of unadulterated tenderness, and the midnight ride on Nugget’s back, naked, bounding with his ‘manbit’, ‘horse-cream’ in his mouth, and spurred on by Dysart’s cry of ‘Mount him!’, is orgiastically infectious. This production’s sympathetic approach to the gay subtext lays bare Dysart’s own repressed homosexuality, and makes perfect sense of his confession that he envies Strang, even as he avoids intimacy with his own wife. Sexual acceptance, creativity, and God enjoy a simultaneous orgasm. Which is nice.

Peter Shaffer may have turned guilt into an art form. This production offers a glimpse of forgiveness.