Rising stars are what every theater troupe hopes to discover and nurture, but this week’s openings are a reminder that old pros count, too. Having them around can burnish a production, provide continuity to a season, and resonate with the crowd out front in ways no batch of fresh faces ever will.

This used to be the not-so-secret strength of our major repertory companies—the play might be unfamiliar, but a regular stable of actors ensured the experience of watching it would not be. These days, with standing rep companies a thing of the past, this brand of continuity is more often honored by our smaller troupes than our more established ones. When hulking Brian Hemmingsen arrives on stage in Forum Theatre’s The Illusion, making his way by glow of cellphone and growling that he seeks a sorcerer, and Nanna Ingvarsson emerges barefoot and wild-eyed from behind a scarlet curtain to help him find the son he drove away, they trail all sorts of associations: Beckett, Ionesco, Chekhov, dozens of roles in more than 30 years they’ve performed both in tandem (they’re married offstage) and apart.

Does their presence ground a show that’s about to get all hifalutin’ about love, magic, and theater? For sure. In the one-ring circus that is Tony Kushner’s adaptation of Corneille’s 17th century comedy L’Illusion Comique, she will conjure and he will observe as younger performers play out the sort of romantic fantasies in which they once took the leads themselves. Watch their faces as the others finagle and fuss through a series of variously disastrous assignations, and you’ll know all you need about the folly of love. Director Mitchell Hébert has given the young lovers some clever business—wait’ll you see the staging fillip with which he sets up a line beginning “on the other hand”—but nothing he’s done is more apt to rivet you than the fact of these two sitting on the sidelines.

The raptness of their attention turns out to be central to what you’d have to call the play’s trick ending. But it’s also fun in its own right, whether Hemmingsen’s interrupting the action to protest that it makes no sense, or Ingvarsson’s orchestrating the ticking passage of time (Aaron Bliden, giving his tongue a workout).

The comparative youngsters at center stage are also accomplished—Mark Halpern as a malleable, curly-headed, Candide-like innocent, Brynn Tucker as the fiery, aristocratic lass he’s wooing for all the wrong reasons, Joe Brack and Gwen Grastorf as calculating schemers with designs of their own, and a deliciously hammy Scott McCormick as a poet who more than lives up to someone’s description of him as a “monster of ego.”

Names change, and character traits do, too, partly for reasons I shouldn’t reveal, and partly because Kushner’s so in love with language that he can’t resist putting new sounds in everyone’s mouth every minute. Too many minutes, let’s note—the evening, even paced at a gallop, runs longer than it should. But it’s easy to understand why no one wanted to cut a script in which love will be referred to as a “hydra-headed gargoyle” for the sheer joy of saying those words.