PRESCRIPTION THUG Thornton makes trouble for himself.

As an Irish thug recounting the day his life went to hell, Michael Patrick Thornton delivers what may well be the most interesting performance currently on a Chicago stage. It’s tempting to make this the story of Thornton’s near-fatal strokes in 2003, which left the young performer having to relearn to walk and talk. As undeniably significant as that recovery’s been for Thornton, and as undeniably powerful as it is to see him slowly make his way onstage with a walker, it’s also utterly beside the point. Thornton infuses his monologue with a rich complexity highly uncommon for any actor.

While the hired hooligan narrates a routine job that turns into a killing and kidnapping spree, Thornton, seated throughout, fascinatingly conveys the thief’s ever-shifting, often-conflicting states: both brutal and vulnerable. Brian Sidney Bembridge’s lighting and abandoned-warehouse set focus our attention solely on Thornton’s astonishingly expressive face; he transforms from tender boy to rough man with the subtlest shift in his eyes. And his pauses, though underused, suggest a depth of feeling that this character can’t express through the crude language at his disposal. It’s a testament to Thornton’s skill that we don’t quite notice that McPherson’s hour-long monologue, while an actor’s chew toy, retreads well-trodden territory: The hardest lout can have the softest heart. (And Thornton and director Gawlik could better handle the tonal transitions.) Yet, hopefully Chicago companies, when casting roles normally reserved for the able-bodied, will consider an actor with an unusual frame—and an even more unusual talent.—Novid Parsi