By Clare Bevis

This should be a difficult play to enjoy. And I actually do mean should: Equus is based on a real crime that Peter Shaffer once heard about in passing; a teenage boy who blinded six horses with a metal spike.

"I had to create a mental world in which the deed could be made comprehensible," he said. But this week's OFS production is…fun. It is essentially a detective story: a boy called Alan Strang mutilated six horses with this spike, and you're there to find out why he did it.

Haven't we seen this man somewhere before? Colin Burnie in his latest role

The fault actually lies in the writing, not the production team. It just isn't an intelligent play. Shaffer was determined to make madness comprehensible, but he made it too comprehensible, made every neurosis fall into place, and his explanation is - well, a bit lame.

Shaffer doesn't want to deal with the real human mind. The most brilliant parts of Equus were the scenes between Alan and his doctor. Here, quick fire dialogue and extraordinary dynamic re-enactments with dancer-horses make it obvious, blindingly obvious that Alan is in terrible pain, but that he is awakening through the course of his treatment and through the relationship with Dysart. Dysart responds; he also grows. Actors Andy King and Mike Bartlett are at their best right there and the play becomes lovely, beautiful.

But Shaffer buttons down the conclusions. The audience is directed into a specific debate: is madness better than sanity? Equus closes not with Alan, exhausted, sated, for us to make of what we will; but with Dysart bemoaning the dull normality of adult life. Shall we ever feel passion again?

Equus feels like a detective story because it is: the cleverly constructed plot which makes it so much fun is just a mirror of the cleverly constructed psyche which apparently makes a boy stick steel into the eyes of a horse.

It is, really, enormous fun - and I plead with you to laugh out loud in the scene just before the interval, because I'm sure that's what the actors wanted - but it left me frustrated. It's a great production and the energy would be there to make it something amazing, if the writer was honest enough or brave enough.