As a teenager, Jerry Hearn saw the play at the Old Vic and found it a very powerful work. He was cast as Dysart in a production several years ago but it had to be cancelled and is relishing the opportunity to play the role at last.

"It's just an extraordinary experience," he says.

Hearn has long been a fan of the playwright and says, "Shaffer's just the most extraordinary writer ... the language is beautiful and he uses the theatre in the most extraordinary way."

The audience meets Dysart right at the start as he introduces himself and the compelling experience he has had with the Strang case.

"That experience is the play."

And while on the surface it might seem to be a case study of cruelty to animals, as he probes deeper Dysart finds there is more to what happened.

"He digs to find some meaning, a sense of ritual, awe, wonderful and worship - but not religious as a churchgoer would recognise."

One of the things Dysart discovers is that Alan's parents have divergent views on religion - his mother Dora (Nikki-Lynne Hunter) is a devout Christian while his father Frank (Ian Croker) is an atheist. Alan has channelled his spiritual fervour into horses, creating a God-like figure, Equus.

The creatures are present in a symbolic way with actors in stylised horse costumes.

Hearn says, "There are masks through which you can see the actors and artificial hooves, and they move like animals."

One of Dysart's interests, revealed during the course of the play, is ancient Greek history, and characters - human and horse - when not directly involved in the action sit on the side of the stage in a manner reminiscent of a Greek chorus.

"They don't comment on the action in the way a chorus does but they are emotionally involved in what's shown."

Director barb barnett says Peter Shaffer's play is "rooted in incredible symbolic intent. Shaffer's a really interesting writer with an incredible directorial eye".

His work, she says, is full of ritual and imagery that can communicate powerfully to an audience as well as the story itself.

"He's working on two different levels simultaneously: he's working with the characters and the storyline and using commentary to the audience."

And while young Alan might be seen as a disturbed youth, Dysart is also a deeply troubled man, questioning what he is doing with his life and how much his work with young people really helps them.

"I'm a big fan of Shaffer, the way he controls the story," she says.

"I'm a great believer in realising what the writer is saying and being incredibly honest and truthful to that writer."

And with Equus, she says, she is working with a great play containing clear instructions from Shaffer on how he wants it performed - and one that can only have justice done to it in the theatre, where it can enthral an audience at every performance.

She sees the 1973 play as the middle of a thematic trilogy that began with The Royal Hunt of the Sun (1964) - about the conquest of Peru by the Spanish - and ended with Amadeus (1979), which dealt with the rivalry between composers Antonio Salieri and Wolfgang Amadeus Mozart. In each, she says, there are two central characters, one marked by a kind of brilliance or passion, the other envious of this because they are empty in some way.

"The tragedy of Dysart and Alan is that it's not a battle of right and wrong but two different sorts of right, but it is impossible for them to co-exist."

Equus. By Peter Shaffer. Directed by barb barnett.Canberra Repertory Society. Theatre 3, September 25-October 11. Tickets $40/$35. Bookings: canberrarep.org.au