"Breaking the fourth wall" is a pretty hoary concept in theater, but Dan Jemmett's approach to it is refreshing. As he demonstrates in his latest Quantum collaboration, the British-born director exploits the fourth wall at once so casually and so thoroughly because we are never sure that he even acknowledges its existence.

Like much of Jemmett's work, the recently wrapped Museum of Desire has for source material a non-play that suggests no easy route to the stage: It's based on a short story, by John Berger, about looking at art in a rural French museum. Through his usual semi-improvisational creative process, Jemmett and his cast -- most of whom conspired with him on last year's raucous The Collected Works of Billy the Kid -- arrived at a structure wherein the actors take turns as the narrator and also together explore selected exploded moments of the story.

Staged in a gallery at the Frick Art museum, some of these sequences are wonderfully theatrical in a classic sense: barrel-chested Rick Kemp transforming into a horse before our eyes; Kristin Slaysman and John Jay wordlessly desiring each other from afar. Other strategies for shattering the invisible barrier that conventionally divides spectators from actors include having the two halves of the crowd seated facing each other (making us both watchers and the watched) and dispatching the actors at one point to "inspect" audience members as though they were artifacts, even to the point of infringing on personal space.

Like a sequence that's a self-concious tableaux (it might be titled, "The Company Harks to Distant Music Heard Faintly Through a Door"), these passages all of course serve to emphasize the artifice in art. A few other moves,  though, were pure Jemmett, and seemed to peel back layers of experience (or maybe just meta-experience) one hadn't been quite sure existed. For instance, while the play's action was continuous, and intermissionless, often a "scene" suddenly leapt to life with an actor hitting "play" on an old-school desktop-model cassette-player; the chamber music then scored the subsequent action ... which abruptly halted when someone hit "stop." (Were the cassette-handlers in character or out, and does it matter?)

Best of all, I think, the show's first half ended with each of the performers exiting singly, on lines of Berger's ruminative prose, never to return to the gallery. Their failure to return, even for a bow, is a very rare thing, even in experimental theater, and it made even more palpable the play's sense of unfulfilled longing, of people passing into History and Time. ("To be desired," writes Berger, "is the closest anyone can come in this life to feeling immortal.") Then, after all this angularly elegant play -- and a long, pregnant pause -- a decidedly rumpled Jemmett himself strolled into the gallery to hit "stop" on the player one last time, and to tell us to go look at the 16^th-century drawings in the next room during intermission.

The show's second half was über-traditional: In the Frick's little dollhouse-like theater, we were treated to a casual literary reading (by Jemmett, of another short Berger story about art) and a gorgeous performance of Schubert's piano quintet "The Trout" by a CMU student ensemble.

During the intermission, by the way, Jemmett wandered the galleries, offering guests wine gums (little British candies) from a silver tray. The candy had been mentioned in "Museum," and -- like the shots of whiskey the audience got to knock back during Billy -- it too connected us sensually to an imaginary world.