Curled up in the foetal position in the faraway corner of a hard floor, boxed in by a wall of white curtains which billow in the breeze with a hint of menace, who we presume to be a patient or an inmate slowly reveals himself to be an “overworked psychiatrist in a provincial hospital” sporting a beard-stroking look of curiosity mixed with doubt.

So begins director Ned Bennett’s stripped-back and striking production of Peter Shaffer’s Tony Award-winning play for Theatre Royal Stratford East and English Touring Theatre which transferred to Trafalgar Studios following a short if well-received tour.

The grounds for Martin Dysart’s (Zubin Varla’s) doubt, which after a lengthy confessional is recounted in chronological order through conversations with his magistrate friend Hester Salomon (Natalie Radmall-Quirke) and flashbacks of his “Nosey Parker” investigations, being the admission of 17-year-old Alan Strang (Ethan Kai) – not quite strong, erring towards strange – who has been charged with blinding six horses with a metal spike.

But it’s not the shocking nature of the case which confounds him, nor indeed the erratic behaviour of his patient both in and out the “torture chamber” of his practice, but the unbridled expression of Alan’s passion together with his accusatory stare which forces him to reflect with increasing disappointment and jealousy on his loveless marriage to his “drizzly kirk” of a wife, the stultifying nature of his job, which he describes as “unworthy to fill” him and the lies he tells himself and others in order to get through the day.

Having premiered in 1973, the themes of Peter Shaffer’s iconic play are as relevant now as ever. With the banality of mainstream entertainment and the automation of modern life put sharply into focus through the brisk wheeling in and out of a soul-sapping TV and deafening hoover.

Zubin Varla is quietly impressive in his measured portrayal of the self-questioning shrink who only erupts once when Alan invades his personal space to take what is not his. Ethan Kai delivers the perfect mix of naive vulnerability and seductive danger; his awkward disrobing at the hands of the more experienced Jill (Norah Lopez Holden) symbolising the freeing of (if not freedom from) his demons – in stark contrast to his buttoned-up parents Frank and Dora (Robert Fitch and Doreene Blackstock). And Ira Mandela Siobhan’s physical transformation into the equine object of Alan’s affection Nugget is as erotic as it is transfixing.

Bennett, together with set and costume designer Georgia Lowe, keeps it simple and the production is all the more powerful for it: a white-powdered square fenced in by cubical curtains; with minimal props, including a fast-revolving hospital bed with a trampoline mattress, moved in and out of position with clinical precision. And Jessica Hung Han Yun backlights proceedings with a rainbow of colours to match the mood music of Giles Thomas’s score. The combined effect of which is that Shaffer’s words and ideas take centre stage and invite us to consider Dysart’s conundrum: what is normal?

Peter Callaghan