In American Century Theater's "Machinal," mother's little helper is a bottle of pebbles that she uses to kill her husband. Based on the story of murderess Ruth Snyder, a photograph of whose execution in 1928 was published in the New York Daily News, "Machinal" is playwright Sophie Treadwell's tense, fascinating portrait of a woman come undone.

Snyder's crime has also been fictionalized in films such as "Double Indemnity" and "The Postman Always Rings Twice," both of which portrayed the wife as a cold-blooded femme fatale. Treadwell takes a more sympathetic approach, focusing on the unhappiness of her antiheroine, Helen, and glossing over the violence entirely, instead recounting the incident in a trial at play's end.

Treadwell wrote "Machinal" in 1928, but the drama's criminal-as-victim viewpoint, as well as its depiction of a suffocating city lifestyle, seem quite modern. The action takes place in nine episodes, beginning with Helen's morning commute to the New York office where she's a stenographer. Helen (Marni Penning) is having a very bad day, but you get the impression that all her days are bad. She arrives at her workplace flustered and late, and when pressed by her gossipy office mates about her constant tardiness, she faults the subway: "All the bodies pressing . . ." Helen begins anxiously.

"I had to get out in the air!"

As grippingly portrayed by Penning, Helen is a breakdown waiting to happen, a submissive sort who reacts to other people's unending demands with tears in her voice.

Helen jumps at the ring of a telephone or an unexpected touch, particularly one from her wealthy boss, George H. Jones (John C. Bailey). Jones asks Helen to marry him, a proposal she grudgingly accepts, though she doesn't love him. "Love? What does that amount to?" Helen's sickly live-in mother (Sheri S. Herren) scoffs when Helen considers saying no. "Will it clothe you? Will it feed you and pay your bills?" Instead of relieving her sense of obligation, Helen simply trades the burden of her mother for the burden of a husband, and soon a child.

The fact that Helen doesn't want any of this is unfathomable to those around her, and Treadwell masterfully designs every scene so that it's clear everyone thinks Helen is as batty as she feels: Her mother repeatedly calls her crazy when she tries to talk about her sadness; her obstetrician condescendingly asks, "You don't want to nurse your baby? Why not?" while Helen lies depressed in her hospital bed, and the caddish Jones, practically a stranger to his virginal wife, can't understand the distress she feels on their honeymoon, trying to calm her with a somewhat sickening: "You're with your husband." Even a restaurant scene, consisting of snippets of conversation overheard at various tables while a performer sings "Am I Blue," subtly reinforces Helen's issues with conformity, as the patrons repeatedly order more drinks with one word: "Same."

Director Lee Mikeska Gardner amps up "Machinal's" tension nicely, frequently having supporting cast members circle the action that takes place in the center of the Gunston Arts Center performance space, an embellishment that sometimes has a practical reason but more often simply mirrors the chaos occurring in Helen's mind. A more unsettling aspect of the production, however, is its generous use of sound, such as the deafening jackhammers that simulate the construction outside Helen's hospital room. "Machinal" may not convince you that Helen's desperate act of violence was justified, but at the end of its tightly wound 21/2 hours, you'll certainly sympathize with her earlier plea: "Let me rest."

Machinal, by Sophie Treadwell. Directed by Lee Mikeska Gardner. Set, Thomas B. Kennedy; costumes, Michele Reisch; sound, Brian Mac Ian; lighting, Marc A. Wright. Approximately 2 hours 30 minutes. Through July 24 at Gunston Arts Center, 2700 S. Lang St., Arlington. Call 703-553-8782 or visit www.americancentury.org.

Marni Penning and John Bailey are the unhappily married couple in "Machinal."