Great performances are rare, great ensembles even more so. One brilliant turn can salvage an otherwise mediocre evening, but when a company of actors clicks, as do the three men who make up the entire cast of Athol Fugard’s “Master Harold” … and The Boys, a great play becomes ineffable, or nearly so: transporting, transfixing and transformative, all at once. That was the impact of this South African playwright’s devastating roman à clef when it opened on Broadway in 1983 with an unknown Danny Glover, Lonny Price and Zakes Mokae, and it’s no less so in the piercing revival that has opened off-Broadway at the Signature Theatre Center with Noah Robbins (Showtime’s Masters Of Sex), Sahr Ngaujah (Fela!) and Leon Addison Brown (Cinemax’s The Knick).

Fugard has had a home for several years at the Signature, and this production is dedicated to Jim Houghton, the theater’s founder and guiding light, who suggested the revival but did not live to see it. In 90 minutes that darken, figuratively and literally, from one kind of dance to another most harrowing, Master Harold captures the evil of apartheid in its most insidious forms: its ruin of black lives but also its corrosive effect on youth, and on hope.

Noah Robbins, Sahr Ngaujah and Leon Addison Brown in "'Master Harold' ... And The Boys"
Noah Robbins, Sahr Ngaujah and Leon Addison Brown in “‘Master Harold’ … And The Boys”
Monique Carboni

The year is 1950, the setting a public tea room on a crummy day in Port Elizabeth, where two servants are cleaning up after the lunch hour. Willie (Ngaujah, a whorl of nature as Fela Kuti) is awkwardly and nervously practicing a dance step, preparing for an upcoming competition he hopes to win with his girlfriend. Watching and teaching is the older, wiser Sam (Brown), who tries, without much success, to get Willie to relax, to enjoy himself, or at least never let them see him sweat. The dance floor, he explains, is the place of escape, where graceful bodies never collide.

Enter Hally, son of the owners, fresh from school and ready to banter before settling down to homework. Hally has been learning by teaching Sam what he brings home from his prep school — about history, politics, science. When he challenges Sam to name the greatest men in history, Sam answers “Jesus,” but Hally won’t allow religion into the conversation; he favors Darwin. Hally, whose mother is tending his crippled, drunken father at the hospital, is intensely familiar with Willie and especially Sam; they’ve pretty much raised him in an unhappy, violence-prone home.

So when a phone call from his mother tells him that they have arrived home despite Hally’s insistence that his father be kept longer, his youthful affection abruptly curdles. He turns his rage on the men who are, in the end, merely his parents’ black servants. He tells a racist joke, to which Sam responds with heart-wrenching dignity. And when Hally demands that Sam, like Willie, address him henceforth as Master Harold, Sam warns him that the breach will be irreparable. Yes, it’s a small, private moment in an out-of-the-way place, and yet the view Fugard suggests of humanity is as encompassing and as bleak as night, as a dance floor on which bodies collide with terrible regularity and consequence.

As with the  original production, Fugard directs without a shred of sentiment, an esthetic that runs through Christopher H. Barreca’s vaguely seedy set, Stephen Strawbridge’s rainy-day light scheme and Susan Hilferty’s effortlessly revealing costumes. This is a fitting tribute to Jim Houghton and a highpoint of the season.

The Irish Repertory Theatre has revived Finian’s Rainbow, the 1947 musical that snuck a potent lefty idea about race relations into a tall tale involving leprechauns, pots of gold and other bits of blarney. Maybe “snuck” is the wrong word, since there’s nothing subtle about the book by E.Y. Harburg and Fred Saidy: In a corner of the state of “Missatucky” called Rainbow Valley, Finian (Ken Jennings) has arrived with his daughter Sharon (Melissa Errico) and a pot of gold pilfered from a leprechaun named Og (Mark Evans) that he hopes to plant near Fort Knox so that it will grow with the rest of the gold there. The good folks of Rainbow Valley, black and white, live free of the racism surrounding them, but their harmonious lives are threatened by the bigoted Senator Rawkns (Dewey Caddell). Comely Sharon, meanwhile, has fallen hard for handsome Woody (Ryan Silverman), who returns the affection. They’re urged along in their romance by their neighbors, including the black “Gospeleers,” who sing like they have a direct line to the Deity.

Ryan Silverman and Melissa Errico in "Finian's Rainbow."
Ryan Silverman and Melissa Errico in “Finian’s Rainbow.”
Carol Rosegg

The plot curves and twists include Senator Rawkins experiencing life as a black man and Og frantically trying to avoid turning mortal until he falls for Woody’s mute sister, the lovely dancer Susan the Silent (Lyrica Woodruff). But of course the real enchantments unfold in one of the all-time great Broadway scores, which includes Harburg and Burton Lane’s  “Old Devil Moon,” “How Are Things In Glocca Morra?” “Look To The Rainbow” (Harburg’s other rainbow lyric) and “When I’m Not Near The Girl I Love” (23 years before Stephen Stills wrote the rejoinder, “Love The One You’re With”).

On the Irish Rep’s tiny Chelsea stage, artistic director Charlotte Moore has fashioned a fleet, intimate (if occasionally disjointed) 2-hour version of the show, and the cast is charming. The star is Errico, who has a gorgeous voice and who previously partnered with Silverman in a fine revival of Stephen Sondheim and James Lapine’s Passion. They sing wonderfully, but the pairing is not as felicitous here. A few months back, Errico wrote a New York Times column about playing an ingénue at 46. I have no argument with the notion of a Sharon who may have been around the block a few times, yet I can’t help but wish the same applied to her Woody. They struck me as mismatched and unsparked.

I also wish Moore had deployed her fine actors with a little more attention to one another and less attention to me: Much of the show finds the principals singing directly out to the audience (often, in Errico’s case, front-and-center). Look at one another! You’re adorable!