The 1968 play “The Boys in the Band” – both pioneering and polarizing for its simultaneously honest and stagy depiction of pre-Stonewall-era male homosexuality – gets a handsome, impeccably acted Netflix film adaptation by director Joe Mantello based on Mantello’s 50th-anniversary Broadway revival in 2018.

As a film, “Boys” is no less bound by theatrical artifice today than William Friedkin’s 1970 film version was. Despite a screenplay tweaked by Ned Martel, using flashbacks and prologue vignettes to open Mart Crowley’s single-set story, it still feels very much like a writerly construct housing an acting showcase. (Martel was a Washington Post editor and writer from 2009 to 2012.)

But oh, what a showcase it is. The ensemble cast, reunited from the 2018 production, is never less than mesmerizing even in the context of what is essentially a museum piece. “Boys” takes place over the course of a single hellish evening in a New York apartment in which several friends have gathered to ostensibly celebrate a birthday – but which devolves into a group-therapy session featuring recrimination, accusation, apology and confession.

The plot centers on Michael (Jim Parsons), the party’s 40-something host and a recovering alcoholic wrestling with Catholic guilt and other demons, all of which scramble out of his psyche as bitterness and booze loosen his inhibitions. “Turning … turning,” repeatedly intones the vain birthday boy, Harold (Zachary Quinto), as Michael’s mood gets nastier and nastier, until, when the curdling of conviviality has reached its full flower, Harold announces: “Revolution complete.”

The party by this time has moved indoors from Michael’s rooftop patio after rain arrives to spoil the fun. But the real storm is psychological as Michael hits on forcing his guests to participate in a parlor game in which each must telephone the love of his life to declare his affection. Some of these monologues are among the film’s most poignant moments.

Through it all, other tensions periodically flare up and subside as a couple (Andrew Rannells and Tuc Watkins) bicker over monogamy vs. promiscuity; Harold and others insult the intelligence of the dim but pretty rent boy (Charlie Carver) one guest has purchased as a birthday present; and an unexpected guest (Brian Hutchison) – presumably the soiree’s lone heterosexual – punches out another party guest (Robin de Jesús) for camping it up too much, as Michael puts it.

There’s no escaping the dated nature of this story. Certain lines might set your teeth on edge, as when Michael announces that gay men are “worse than women about their age.” There also is no escaping dialogue that comes across, at times, as preachy: “If we could just learn not to hate ourselves so very much,” Michael says late in the film’s third act in an articulation of a sentiment that is by that point fairly obvious.

“Boys in the Band” is best when it shows rather than tells. Mantello does a good job of illuminating how the twin pressures of societal homophobia and internalized self-loathing deform the human spirit, until it takes on the shape of something monstrous.

Michael’s boyfriend (Matt Bomer) is in psychotherapy and on Valium. Other characters talk about suicide and joke, with caustic humor, about having to butch it up in front of heterosexual people. Living in the closet will turn you into a kind of emotional hunchback, the film seems to argue.

In 2020, there is, sadly, nothing anachronistic about that truth. In the film’s final image, Mantello shows Michael running down a street after the rain, away from the camera – and, as it were, toward a future that holds both promise and, overlaid with the film’s pall of pessimism, the long shadow of persecution.