Bebe Neuwirth gives a master class in acting at Philadelphia Theatre Company’s new play, ‘A Small Fire’

Bebe Neuwirth, star of television (Cheers) and stage (Chicago), gives an unshowy but heartbreaking portrayal of a woman who literally loses her senses — from her sense of taste to her eyesight — in Philadelphia Theatre Company’s production of A Small Fire (through Nov. 10).

Director Joanie Schultz’s staging of the 85-minute Adam Bock play is nuanced and fiercely naturalistic. But the work itself toggles uneasily between the world of realism and some darkly fantastical realm, leaving audiences (much like the people in the afflicted woman’s orbit) unsure just how to react.

Set in Connecticut in 2011, the play focuses on the unexplained disaster that progressively disables construction company owner Emily Bridges (Neuwirth), and how she and those closest to her react to it.

We meet Emily in a dark pantsuit and white hard hat, a vaguely unpleasant, profane, stress-inducing woman in charge. Demanding at work, critical of her daughter Jenny’s impending husband (a mere importer of cheese), and bored with her own, she must surrender all her hard-won control as she takes leave of her senses.

More precisely, they take leave of her, one by one. The titular small fire is what ensues when Emily, having lost her ability to smell, can’t detect smoke.

Soon, however, a metaphorical conflagration envelops her, rendering her unable to do much more than talk and feel. And who knows what will happen to her next, after the curtain falls?

The production is beautifully lit by Rachael Cady, with a fluid and functional set by Chelsea M. Warren, costumes by Mark Mariani, and sensitive sound design by Christopher Colucci.

But above all, under Schultz’s direction, it is a master class in acting.

In Neuwirth’s devastating portrayal, Emily grows increasingly isolated, sadness etched on her face, nervous energy evident in hands that can’t stay still. The formidable John Dossett, whom PTC audiences saw in 1998 in Paula Vogel’s How I Learned to Drive, plays Emily’s nurturing, underappreciated husband, John, with warmth, compassion, and a dash of bewilderment.

Oge Agulué is more vivid still as Billy Fontaine, Emily’s construction manager and best friend, whose hobby is racing homing pigeons. Barrymore Award-winner Sarah Gliko (The Bridges of Madison County) dares to be unlikable as Jenny Bridges, whose strongest impulse is to flee.

Bock’s off-kilter sensibility keeps the audience guessing, suspended between comedy and tragedy, and we’re not entirely sure what to make of Emily’s multiplying afflictions. Is this a health-crisis play, like Wit (cancer), The Waverly Gallery (Alzheimer’s), or The Normal Heart (AIDS)? Can anything be done to help our protagonist?

Or have we wandered into the territory of absurdism, where characters metamorphose into rhinoceroses (Eugène Ionesco)?

Tony Kushner managed a brilliant mash-up of AIDS and the supernatural in Angels in America, but that was on a far more expansive canvas. In this modest work, the formal ambiguity is less satisfying.

As it happens, AIDS comes up in A Small Fire, too, when Billy reveals to John Bridges that his first romantic partner succumbed to the disease.

Having survived loss and found love again, he eloquently delivers the play’s message: “This can be a disaster or it can be an opportunity. … You gotta live a little bigger than you think you can.”

A Small Fire

Philadelphia Theatre Company production through Nov. 10 at the Suzanne Roberts Theatre, 480 S. Broad St.

Tickets: $25-$74.

Information: 215-985-0420, philatheatreco.org.