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Calling your story “Melancholy Play” is a bold move; you’re claiming a whole emotion. But using that title ironically, for a comedy, is even riskier — better earn that dissonance.

Melancholy Play: A Contemporary Farce, written by Sarah Ruhl, directed by Nick Martin, and going on now until September 2 at the Source Theatre on 14th Street, is so funny, it’ll make your cheek muscles sore. Indeed it deserves that ambitious title. But it earns everything else about itself, too. It’s ridiculous, it’s surreal, and it’s nostalgic and wistful for things that maybe never happened.

Meet Tilly (Billie Krishawn). She’s a beautiful and beguiling bank teller with a very interesting condition. She suffers from a form of sorrow and dolefulness so romantic and seductive that it both entrances and infects all those who meet her. Well, “suffers” isn’t quite the right word, because Tilly (and yes, she’s in therapy), despite crying at the drop of a hat and spending hours staring mournfully out the window, seems to rather enjoy the despondency. Everyone else sure does: All the men and women in Tilly’s life fall in love with her, from her tailor and her hair dresser to her hair dresser’s girlfriend. As one of them puts it: “She turns her sadness into this sexy thing!” Call it triste de vivre.

This is one of those casts where everyone seems to be in a competition over who’s the funniest — a competition the audience wins. Krishawn, who has to cry a at several different junctures, is anything but a wet blanket. She brings to Tilly a warm empathy, even when she’s sprawled across the blue chaise lounge at center stage. As her therapist from “an unspecified European country,” Christian Montgomery rises above his silly accent to deliver truckloads of punchlines. As British nurse Joan, Lilian Oben is brisk and efficient, with a hilarious deadpan; her stare could stop a train. Mary Myers’s Frances runs the hottest — her own mopes drive the play’s final minutes — and she gets maybe the biggest laugh of the night, turning the simple statement “I moved” into an epic proclamation. And John Austin’s Frank is gut-busting in his helplessness as the only one of Tilly’s admirers whose affections she returns. All five actors are a scream with both dry wit and broad hysterics. Well done.

This story, in case it’s not clear, is not entirely set in reality, though it does seem like they get philosophical postcards from there. The set, designed by Jonathan Dahm Robertson, includes a wall of empty window frames in front of a backdrop of doors painted with blue sky and white clouds reminiscent of Magritte, a painter who gets name-dropped. Ceci n’est pas une melancholy. The costumes, from Kitt Crescenzo, are prim in a pleasantly dated kind of way: the nurse wears a white cap and a navy cape; the hair dresser does her job in boots with a heel. They might call it Illinois, but in Melancholy Play, we’re across some misty ocean.

The world it creates is almost childlike in its way. There’s no cursing or alcohol or substances. The sex is referred to only as “we made love” — and the actors leave their clothes on. But the existential crises, and equally high-risk comedy, is very much adult.

At a certain point, people become so sad, they start turning into almonds. Just gonna leave that one there…

How all these ingredients combine into such a winning confection is better seen than described. Even those who are already fans of Ruhl’s work as a playwright may be bowled over by what they find here. D.C.-area theatres are just now awakening from their summer hibernations, kicking off their 2018-2019 seasons. The Constellation Theatre Company, which is still too young to be in high school if it were a person, can claim a rock-strong opening gambit.

Don’t let the name fool you — you will walk out of this play brimming with joy.

Melancholy Play: A Contemporary Farce runs until September 2 at Source Theatre