Usually before a play, a disembodied voice warns theatergoers against using cell phones or unwrapping cough drops. But before “Haymarket,” Zayd Dohrn’s oddly sleepy new play, the voice actually says, “There will be bright lights and abrupt noises in this play.”

So much for startling your public. Must companies now treat theater audiences like baby chicks in an incubator? Before Ibsen, will someone say, “The following may contain unfortunate incidents with a duck”?

Most of “Haymarket” seems like gentle preparation for an impending explosion. But the boom never comes, and director Robert Saxner wraps every moment in cotton wool. Written about the aftermath of the 1886 Chicago Haymarket riots, the play recalls events that terrified the nation, led to one of our country’s most shameful legal miscarriages, and crushed the labor movement for more than a generation. It features reeling, bloody policemen, a lunatic asylum with vicious orderlies, and a public hanging. Somehow, this production remembers these events wistfully, with no outrage and no adrenaline.

Sitting on a plain bed in a windowless room, Lucy Parsons (Squeaky Moore) has just been committed to an insane asylum. Her doctor, an ahead-of-histime psychotherapist (Morgan Baker), thinks he can help her by interviewing her about her infamous parents.

Lucy’s mother, labor advocate Lucy Parsons (also Ms. Moore), and father Albert (Dennis McNitt) were major figures in Chicago’s 19th-century anarchist movement. After an unknown protester threw a bomb at police during a political rally, a hysterical city sentenced eight anarchist leaders to death in a trial more concerned with the defendants’ pro-labor views than their guilt. Lucy’s father’s martyrdom (Albert hanged with four others) has clearly driven Lucy partially insane – and we have the redtinged flashbacks to prove it.

This framing device has very little bearing on “Haymarket” – though the younger Lucy sometimes hovers in the background, cooing or tracing imaginary lines on her walls. Ms. Moore has much more to do as the older Lucy, a tough-minded activist who has no time for human frailty. When Albert, knowing his life will be in danger, flees to Wisconsin, she soon calls him back to stand trial, believing his appearance will benefit the movement.

Before long, every storyline has turned domestic and sentimental. The couple’s marriage begins to falter, and a tentative extramarital flirtation takes place. We do meet other victims of the riots – a policeman who has gone deaf from the blast, a nurse grieving for her dead brother – but even these two embark on a fledgling romance.

Mr. McNitt, Birgit Huppuch (as both the nurse and Albert’s inamorata), and Judson Jones as the deafened cop all do sensitive, understated work. The trouble lies in piling them up into a twohour block. After scores of scenes, all of which strike the same pitiful note, I felt like tossing a dramaturgical grenade.

Until December 23 (410 W. 42nd Street, 212-279-4200).