What is passion? Is it an undying, brightly burning, love, an act of worship? And if so, what is the price of worship?

Equus, the perennially popular play first staged almost fifty years ago, tackles these issues head-on, and this new production at the Theatre Royal is particularly visceral in its interpretation.

Alan Strang (Ethan Kai) is a 17-year-old boy, speaking only in TV ad jingles as he is confined to a mental institution following a horrific case of animal abuse. Dr Martin Dysart (Zubin Varla) is his therapist, initially struggling with the boy’s wilful aggression towards his attempts to help, but soon discovering Alan’s deeply warped, black twisted faith.

What follows is an enveloping journey through a troubled psyche, leaving the good doctor questioning his own life and values – for what mortal love could compare to that love which Alan feels for Equus, his horse god?

Ethan Kai is terrific as the cocky, insouciant and troubled teenager, while Zubin Varla is convincing as a mostly-committed realist nonetheless struggling with the relative mundanity of his existence, and the nature of his work as a child therapist.

But special mention must be given to the ‘horses’ themselves, with Ira Mandela Siobhan leading. Clad in sports underwear, rippling with muscle, they are remarkably equine in their movements and tremendously believable as objects of lust for the confused boy. This inventive spirit continues throughout the production, with trampoline beds, sandcastles and more granting a sense of experimentation and a mundane physicality to compliment the sometimes-fanciful dialogue.

Twisted, devastating, visceral and occasionally unbearable, Equus is simply extraordinary.

Equus runs at the Theatre Royal Bath until April 6 - Marion Sauvebois