‘The Castle” might seem closer in spirit and structure to an Alcoholics Anonymous meeting than a dramatic play, but it is reliant upon that time-honored theatrical device, the personal narrative. Four recently released former prisoners recount their lives, with only their chairs and their music stands to accompany them. The effect is more harrowing and powerful than that of most other prison dramas and activist plays.

Casimiro Torres, Angel Ramos, Kenneth Harrigan, and Vilma Ortiz Donovan are not celebrated actors. Prior to “The Castle,” they weren’t even performers. Their delivery is phlegmatic, and the downward spiral of desolation caused by drink, drugs, and poverty that they speak of hardly constitutes a new message. But it’s not difficult to see why “The Castle,” co-written by the cast with director David Rothenberg and performed each Saturday, has kept extending its run since it opened in April at New World Stages.

All four individuals ended up in The Castle, a nonprofit Upper West Side rehabilitation center that until the 1970s was a Catholic girls’ school. The burly Torres commands the most effective stage presence. Arrested 67 times for drug-related crimes, he served 16 years in prison before a return to Rikers Island finally set him straight. His deep, guttural voice resembles Al Pacino’s during his earlier, non-shouting phase. “By the time I was old enough to choose, I never had the choice,” Torres says, recalling his Manhattan and Brooklyn upbringing. “I was getting high at the age of 10.”

Harrigan, who spent 16 years in prison, also possesses an assured stage presence as he describes how rejecting a basketball scholarship to pursue his dream of being a deejay led to a crack cocaine addiction and being incarcerated for burglary. Faith in God and studying law proved his salvation.

As when Harrigan recounts how a parole officer blocked him upon his release from living with his future wife, another former prisoner, an undercurrent of anger runs through the performers’ discussion of wrong choices and missed opportunities. For the most part, though, they avoid heavy-handed preaching or excessive self-pity.

“The Castle,” in simple and eloquent fashion, subverts preconceptions. Ramos, smartly dressed in a suit and tie and speaking in a low-key manner, could be a sheepish math professor. Yet he spent 30 years in prison for murder before discovering that his forte lay in computer programming. Upon his release from prison, he had a birthday party for the first time at the age of 48. Donovan, the least articulate and most emotive of the quartet, is an erstwhile disco wild child, whose drug dealing led to two separate terms in state prison.

Don’t look to the play for prison-reform solutions. The only answer the cast proffers is predictably high regard for The Castle, operated by the Fortune Society, a nonprofit organization that assists the rehabilitation of prisoners.

Still, New York is full of people who look and act as though every day is an immense ordeal and that their world will end tomorrow if they don’t get their way. But how often do we hear from those who genuinely have been imperiled but have since taken pride in becoming taxpayers, as opposed to hearing from actors and dramatists who speak for them?

The testimony of the ex-inmates in “The Castle” brings to mind F. Scott Fitzgerald’s counsel never to confuse a single defeat with a final defeat. To hear this quartet speak of their eventual victories over their demons makes for insightful and affecting theater.

Until September 27 (340 W. 50th St., between Eighth and Ninth Avenues, 212-239-6200).