Local playwright Holly Arsenault's full-length debut, Undo, has a premise so deliciously simple, it's a wonder it hasn't been done already: What if there were a requisite divorce ceremony, a sort of backward wedding, where the original guests gather to get their presents back, hear the toasts again, see the couple's last dance, then watch them take off their rings and undo their vows?

The idea makes a cruel kind of sense: Weddings turn a private thing public; they ask a community to witness and endorse what has up till then been a personal arrangement. If you want to dissolve it, why keep that part hidden? Everyone helped you get to the altar; maybe they should help carry you off it, too. (Some smart Hollywood person is surely already on the way to knock on Arsenault's door.)

Thankfully, Undo isn't a "great concept, poor execution" scenario. The script is fantastic, with witty but believable dialogue that sounds cribbed from real family get-togethers and focuses on the small, mundane logistics of the un-wedding that make it so convincing—the mother of the bride (Barbara Lindsay) obsessing about whether her daughter is wearing the right underwear because "God is watching," the ex-girlfriend of the best man coming as his date just to be polite. In the background, a boy glues together a shattered glass cup—it was a Jewish wedding. The bride (a breathless and detached Sydney Andrews) stares vacantly into space, trying to figure out how she got to this point. The groom (Ashton Hyman, puppyish and wounded) is still trying to call off the ceremony. Around them, like at any big event, the scope expands from tiny details (flowers, outfits) to massive intergenerational dramas (the reverberations of a shotgun wedding from the 1940s). Surefooted and funny, Undo will undoubtedly be trimmed and shaped further, but it's hard to imagine this play not going somewhere after its Annex debut.