A scene from IMPOSSIBLE! A Happenstance Circus. (Courtesy Round House Theatre)

An escape artist gets locked inside a water tank in “Impossible! A Happenstance Circus,” and it’s ridiculously suspenseful and witty because . . . well, there’s no actual water. It’s all pretend.

That’s the magic of this 75-minute show, which is as easygoing and charming as they come. Maybe you saw the high-tech, bombastic “The Illusionists: Witness the Impossible” on Broadway or at the Kennedy Center, which featured a guy trapped in a real water tank, holding his breath forever as he tried to wiggle free. The puckish simplicity and inventiveness of the Happenstance version is actually more fun.

Happenstance Theater specializes in the old skills — physical theater, clowning, mime — all served here with winking whimsy. They are pros: There’s a lovely formality to this performance, a precision of movement and a deliberate pace that’s in line with Charlie Chaplin, Buster Keaton, the Marx Brothers.

They fool around with shadows. They play mirror games. They walk on high wires that aren’t there. The six actors, led by co-artistic directors Mark Jaster and Sabrina Mandell, have a light touch that makes playing along irresistible.

The big stage at the Round House Theatre is bare except for a small tent and a cluttered little station where musician Karen Hansen plays instruments like a banjo and trombone. As Hansen sets moods, the attractions range from sideshow staples (including a hilarious “human pretzel” and a sad-sack un-conjoined twin) to an animal act. The gorilla that waddles out to do tricks with its trainer is uncanny — it’s Jaster, who has clearly spent some time studying at the zoo.

The “theatrical collage,” as it’s billed, was devised by the balanced ensemble, which includes Gwen Grastorf (who warbles a tune while swallowing fire, sort of), Sarah Olmsted Thomas (who brings a dancer’s agility to a high-wire bit) and Alex Vernon (excellent on stilts and in fake mustaches). Jaster and Mandell ring-lead in a variety of ways, none more significant than in guiding the show toward its steady state of winsome humor and grace.

‘Impossible! A Happenstance Circus’

Music arranged and/or composed by Karen Hansen; set design, Alex Vernon, Sabrina Mandell and Mark Jaster; costumes, Sabrina Mandell; lights, Kris Thompson. About 75 minutes. Through July 12 at Round House Theatre, 4545 East-West Highway, Bethesda. Tickets $20. Call 240-644-1100 or visit www.roundhousetheatre.org.