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Blaize Scully (Rusty Clauss), wizened Irish crone, harbors what might charitably be called a low opinion of her daughter-in-law. Here’s the old gal explaining in her braying brogue why the death of her mentally ill grandchild had its roots in her son’s poor choice of a wife: “Because when you breed animal with human, you can only get poor, haunted monsters!”

That’s about the level of subtle nuance and understatement awaiting you in Solas Nua’s disappointingly one-note Irish melodrama, Portia Coughlan. The one note in question is loud and long and so lacking in variation it might as well be the wail of a banshee.

The design team gives it a good crack: You won’t know what to make of Marie-Audrey Desy’s hanging strips of plastic when the house lights are up, but once the actors take their positions behind each one and Paul Frydrychowski aims his blue gels through them, and Chris Pifer floods your ears with the sound of rushing water, the effect is uncanny, even chilling.

And the cast is filled with solid actors doing their very best with what they’ve been given. Stephanie Roswell gives a quietly sympathetic performance as the heroine’s friend that somehow doesn’t get lost in the hurly-burly. Clauss is fun as the old coot, Grady Weatherford and Adam Segaller are memorable in small roles as the title character’s suitors, and Jonathon Church does good work as Portia’s long-suffering husband.

But there’s just too much that’s at once too over-the-top and too on-the-nose. Portia Coughlan is the kind of play that thinks it must name its characters after Greek, Shakespearean, and biblical figures to make sure you don’t miss its mythical themes. It’s the kind of play that uses music to underscore its heroine’s unhealthy obsession with her long-dead twin. The music cues in question? “I Am Stretched on Your Grave” and “You Were Always on My Mind.” It’s the kind of play in which the heroine doesn’t just miss her dead twin (named Gabriel, by the way). No, “The cows bellow for him from the barn on frosty winter nights!”

Playwright Marina Carr’s language is frequently lovely, but when it’s put in service of a tale this overwrought and capital-M Mythic, it just feels pushy and self-conscious. Carr is considerably more generous with the classical allusions than she is with her characters, especially Portia herself, who comes off here as merely shrill.

As Portia, Solas Nua Artistic Director Linda Murray feeds Carr’s penchant for excess. She expresses her character’s deteriorating mental state by stalking the stage with a scowl that Norma Desmond would think needed dialing back. And here’s something director Jessica Burgess should have caught: Murray plays her every scene with husband Church in much the same way: screaming at him while angling her torso forward and thrusting both arms behind her. This is likely meant to be balletic (Murray is a trained dancer), but it occurs so often and so identically that it ends up having a much different effect: It looks like the guy’s arguing with a ski-jumper.