It’s clever for Theatre Exile to mark the debut of its new theater — in its unrecognizably rehabbed South Philadelphia location — with a show both epitomizing and interrogating the magic of transformation.

Tim Crouch’s An Oak Tree, which somehow won a 2007 Obie Award, is about profound loss, the varieties of illusion, and, of course, theater itself. The 70-minute play requires only a bare-bones set (by Colin McIlvaine) and relies heavily on a single (to me, tiresome) gimmick: One of its two actors has never seen the script and supposedly has no idea in advance what the show is about.

The corollary is that the part in question — a father whose daughter was killed in a traffic accident caused by a hypnotist — must be played by a different actor, male or female, every night. The other character — that hypnotist, now very much off his game — is portrayed by Exile veteran Pearce Bunting with a mix of intensity and restraint.

Great, I thought, when I first heard the concept. Long-form improv! With some of the city’s finest actors no less! What fun.

My mistake. Bunting’s character, also something of a stand-in for the director (who is actually Exile founding artistic director Joe Canuso), explains early on: “Every word we speak is scripted.”

Bunting has three ways of conveying the script to the naïve actor: by telling him or her what to say (“Say yes!”), by whispering prompts via a microphone that connects to a headset, or by simply handing over a page or two of the script. The devices are Brechtian — artifice that undercuts the pathos of a death that only imagination, in turn, can make bearable.

“Don’t you think it’s a bit contrived?” the Bunting figure asks at one point. Well, yes, even if the contrivance is the point.

The confrontation between the father and the hypnotist (who, we’re told, doesn’t at first recognize the father) is at once awkward and ludicrous. Crouch gives the hypnotist a kind of broken patter that emblematizes his decline. The father, remembering his daughter, gets the poetry of grief: “Claire had multiplied. ... She was between lines, inside circles, hiding beneath angles. She was indentations in time, physical depressions, imperfections on surfaces.” (Also, it seems, by way of a mythological metamorphosis, the entire titular oak tree.)

Basically, what the show amounts to is a high-wire exercise for the actor du jour, who must embody the father’s emotions and more with no warning, rehearsal, or thespian equivalent to a net. On opening night, Grace Gonglewski managed the role’s demands with virtuosity and grace.

She’ll be spelled by such Philadelphia favorites as Jennifer Childs, Emmanuelle Delpech, Justin Jain, John Jarboe, Amanda Schoonover, Catharine Slusar, and Dito van Reigersberg. Actors with a national profile include Zosia Mamet (HBO’s Girls) and her husband, Bucks County native Evan Jonigkeit (X-Men: Days of Future Past), as well as Maggie Siff, a veteran of local stages, and her television husband, Paul Giamatti, both of Showtime’s Billions. Giamatti’s March 9 performance is, alas, sold out.

Theater

An Oak Tree

Through March 10 at Theatre Exile, 1340 S. 13th St. Tickets: $10-$50. Information: 215-218-4022, theatreexile.org.