"You're a giver of life," diva Jean says at one point to dirty-jokester Wilf in Quartet, "and that's a lovely thing."

Giving life – especially when you're near the end of it – is the heart of Sir Ronald Harwood's genial, witty play, at Bristol Riverside Theatre through Nov. 19. Quartet rests on a quartet of actors who so inhabit their roles, you can't imagine them as anyone else.

Our scene is a country house in Kent, a retirement home for musicians and singers. Court Watson's set is sumptuous and eloquent, gold-flocked couch, baby grand, ivied trellises on the terrace, and portraits within of Beethoven, Mozart, Giacomo Puccini, and Giuseppe Verdi (affectionately called by his "English" name, Joe Green). Three residents await the arrival of "someone grand," and together they'll face the gig of their lives.

There's Wilf (played by Keith Baker, artistic director at the Bristol; Baker happens to be a real opera singer, by the way). He faces the old guy's agony: sexed up and nowhere to take it. But he's all talk ("I'd like to take you by surprise, while you're bending over, putting on your surgical stockings") and no action. There's Sissy, an audience favorite played winningly by Laural Merlington. Her watchword is "I'm ready," and she is, for men ("I love the smell of male sweat"), friends, music, ever grateful. There's Reggie (done with ideal restraint by Nick Ullett), clear, serious, forever humiliated by a past crashed marriage. And wouldn't you know? The new "someone grand" is Jean (played with zesty snark by Joy Franz), famous diva and the wife who destroyed Reggie. She's now indigent, "on charity," both terrified to be here and in denial. That doesn't keep her from insulting and condescending in all directions.

Quartet makes comedy of old age, with an undertone, beautifully managed by director Susan D. Atkinson, of the inevitable. After the Bristol's traditional pre-show Wednesday night snacks and wine, the audience resonated to a play about people their age. Our four keep eyes on one another, looking for signs of decay, and they're there. Sissy seems especially close to leaving her right senses. Everyone forgets and repeats him/herself. Some signs are hilarious (Reggie's potty-mouthed rage at an attendant who refuses him marmalade at breakfast), some heartbreaking (Jean, realizing she is trapped).

A third throughline, lightly draped, is the meaning of art. Reggie urges the others to see that "it doesn't matter what we sound like," that singing is a "reaffirmation that we're alive." Music can save them in giving them life, enabling each to give life. If they can embrace what they are and be thankful for the music in their lives, they can be, if not happy ever after, at least more accepting of themselves and others.

I won't say there weren't a few slow moments. Quartet is measured, middle-register: It stays within itself. But as its 2012 movie version was, it's a skillful entertainment that makes you care enough. Yes, in life it gets to be too late, but life-givers – music, people, memories, friendship – are lovely things. This quartet give Quartet a lot of life.

Quartet. Through Nov. 19 at Bristol Riverside Theatre, 120 Radcliffe St., Bristol. Tickets: $10-$52. Information: 215-785-0100, brtstage.org.