Peter Shaffer’s disturbing 1973 play about a psychiatrist (Dr. Dysart) who attempts to treat a young man, named Alan Strang, who has a pathological religious and sexual fascination with horses, is one of those theatrical experiences that stays with you. The last time I saw the play was more than a decade ago, and that production still haunts me.

Ludicrous Theatre Company’s production, directed and designed by Wayne Shaw, sets the piece in Nevada. You walk into Boho Theatre’s blackbox space, and you are suddenly in a southwestern stable, complete with sun bleached wood and hay-strewn ground. The actors are already perched in their spots as you take your seat, not unlike horses waiting to be mounted. You can’t help but notice a dude, way upstage, standing on a tiny wooden platform, wearing a horse mask and completely naked. And he (Justin Landry) stands there for 2.5 hours. Yikes. And Kudos.

Aside from the powerfully claustrophobic set and a few costume pieces, the Nevada elements don’t overcome the piece. This is still Equus, in all it’s naked, crazy glory.

As disturbed boy Strang, Ian McCabe is a phenomenal and robust actor. However, his physical stature proves both a strength and a handicap. While it’s intriguing and upsetting to see this big guy emotionally unravel, when it comes time for the climactic act one horse ride, the guy towers over Landry, suggesting more of a pony ride at the county fair than a soul-shredding gallop on a sinuous beast.

But, unfortunately, there’s a more significant problem here, and it’s Kevin Heller’s one-note performance as Dr. Dysart. Maybe it’s due to the cast changes (and other difficulties) Shaw hints it on Ludicrous’ web site, but Heller seemed vastly underprepared for the role on opening night. To be frank, it felt like he was simply reciting lines. (And it bothered me how his arms just hung at his sides for the entire evening.) His performance buried what had the potential to be great — particularly Suzanne Bracken as the empathetic social worker, whose scenes are completely dependent on Heller. She gave as much as she could last night, and I applaud her for that.

While I could usually look past one disappointing performance, Equus is structured in such a way that to have a less than capable actor in this keystone role makes the entire show buckle to its knees.

[Well, perhaps it’s not that dire a situation — the scenes between McCabe and his would-be girlfriend Jill (Kristen Bjorge) hint at the electricity this production could deliver — but it’s pretty darn close.]

But Dysart is our gateway into the world of horse worship, emotional pain and sexual repression. We need him to draw us in, and that doesn’t happen here.

Not even a handsome scenic design featuring a naked guy standing in front of me for the entire 2.5-plus hours can maintain my interest when the acting fails to engage.

“Equus” plays through Nov. 6 at the Boho Theatre in Rogers Park. More info here >