Most of us can probably relate to this situation: You’re on a vacation trip—say, a cruise—and you make a new acquaintance. Between you, casual plans are made to get together again sometime, somewhere, in the future. You probably think it will never really take place. But what if it does? And what if that get-together becomes a true nightmare that upends your whole life?

Such is the scenario behind Steven Moffat’s The Unfriend, making its U.S. premiere at Asolo Rep after productions in the U.K. Moffat, best known as the co-creator of the Benedict Cumberbatch edition of Sherlock as well as a writer on Dr. Who and a version of Dracula, brings his wicked sense of humor to the stage with this debut play, and the show is often very funny indeed.

The unwitting couple in this case, Peter and Debbie (Brian Wallace and Carla Noack), meet up with the super gregarious Elsa Jean Krakowski (Sally Wingert, a hoot), onboard ship, and when she wangles her way into a visit to their London home, they are too polite (being Brits; Elsa’s a pushy American) to fake their way out of it. How bad can it be, anyway? Elsa only plans to stay for a week, and maybe it will even divert the couple from worrying about their awful adolescents, Alex (Zach Harris) and Rosie (Ashley Raymond). They won’t really need her help ignoring their next-door neighbor (Mark Benninghofen), who keeps popping in, because he’s so boring they instantly forget him the moment he leaves the house.

Elsa arrives unexpectedly early, and just after Debbie has discovered something about their houseguest that throws her into a tizzy. I won’t reveal it here, because audiences deserve the fun of finding it out for themselves. Suffice it to say, it’s going to test the couple’s inbred good manners to the fullest.

After a strong and engaging first half hour or so, the play sags a bit in the middle before regaining its full steam for a sometimes hysterical second half (the play runs 90 minutes with no intermission) involving, among other things, some bathroom humor that reminded me a little of Monty Python/Fawlty Towers/John Cleese territory. Moffat, as well as director Peter Rothstein, knows how to build to his punch lines with ever increasing desperation on the part of his characters; I especially enjoyed how Wallace timidly tries to avoid any kind of confrontation as Noack pushes him to act on their suspicions.

The play also gets a lot of help from its music selections (sound design is by Katharine Horowitz) and projection designs (by Greg Emetaz), which add inspired visuals to sometimes over-the-top narration (think TV’s Dateline) and keep us watching during scene changes.

I found some twists implausible (how exactly does Elsa Jean transform the terrible teens into angels so quickly?). But the performances, especially by Wallace, Wingert (pulling out all the stops as the brash Elsa Jean, suitably and flamboyantly attired by costumer Fabian Fidel Aguilar)) and Benninghofen, who makes the most of every mumbled interaction, take us happily along for the ride. You might even end up asking yourself, just how far would you go to avoid social embarrassment? Not, I hope, as far as Peter and Debbie.

The Unfriend continues through March 26 at Asolo Rep. For tickets, call (941) 351-8000 or visit asolorep.org.