If you plan to attend the Winterport Open Stage production of “Black Comedy,” one of two shows running through May 21, you may want to take out laughing insurance. In other words, be prepared to fall off your chair when the lights come up — or when they don’t, as the case may be.

Written by Peter Shaffer in 1965, “Black Comedy” is one of the original shag-a-delic farces. The title refers to the blackout taking place in the London apartment house of artist Brindsley Miller on the evening he is to meet his fiancee’s militaristic father.

To impress the colonel, Brindsley has replaced his own shabby furniture with pieces from the high-dollar antique collection of a next-door neighbor who is out of town. A hard-of-hearing millionaire art buyer is also on the guest list for the night. An unexpected guest, a blast from Brindsley’s past, and a teetotal upstairs neighbor also show up.

You get the picture. In fact, you get the picture more than anyone onstage because while you watch the play in the light, they are moving as if in complete and blinding darkness. Shaffer’s script is brilliant in places, splitting the focus between the stranded guests in the flat and Brindsley stumbling around trying to right some wrongs. The lights are out, but the race is on, and Shaffer charges toward the finish line in high spirits.

It takes some finesse to navigate this outrageous set of circumstances with authenticity. How do you make it look as if you are walking in the dark when in fact the stage is awash with light?

Some actors in the cast answer the question more impressively than others. For instance, Ron Adams, as Brindsley, trips over himself, falls down the stairs and sightlessly tiptoes between two flats with hilarious believability. His limberness is astounding, and his timing is, as always, spot on.

Kent McKusick, as the artsy neighbor, is triumphantly prissy. With his hair bouffed into a pompadour, McKusick is dressed to conquer. His performance shows relentless expertise.

Jenny Hart, as Brindsley’s fiancee, is another gem: teased hair, a full-face pout and a debutante whine. A lesser actor might slip into annoying caricature, but Hart is, in a word, groovy-poo.

The rest of the delicious cast — Molly Lebel as the helpless neighbor, Don Sleight as the colonel, Crystal Vaccaro as the unexpected visitor, Jim Tatgenhorst as an electrician and John Coggeshall as the art collector — hold up their parts with flair, gumption and a terrific sense of corroboration with director Reed Farrar.

These characters may be in the dark, but the audience is entertainingly enlightened about the measures an artist will take to sell his work.

An auditorium setting presents technical director Robert DesLauriers with a challenge that he largely overcomes. Auditorium seating sometimes compromises the sight lines — so the closer the seat, the better the view.

“Black Comedy” is a one-act play that runs over an hour. Farrar has smartly supplemented the evening with an opening show, Christopher Durang’s now classic comedy “An Actor’s Nightmare.” Here, an accountant named George finds himself surreally transported onto stage and inserted into four productions already in progress. It’s an ad-lib nightmare and the poor guy can’t find any explanations for the events going on around him — a modern predicament if ever there was one.

Allen Adams as George has enough physical energy to be in four one-acts at the same time. Sometimes that energy takes him into TV sitcom territory, which isn’t quite faithful to Durang’s writing. Nevertheless, Adams offers no shortage of laughter. Kim Pitula, in several supporting roles, is both statuesque and spunky. Suzanne Hall, Theresa Curtis and Rudy Rawcliffe slip in and out of costumes and attitudes with amusing agility.

In both shows, the audience laughs for all the right reasons — and that’s a true accomplishment for most community theater troupes. Add the bake-sale smorgasbord during intermission, and it’s a night of sweet treats all around.

Winterport Open Stage will present “Black Comedy” and “An Actor’s Nightmare” 7:30 p.m. Friday and Saturday and 3 p.m. Sunday through May 21 at Wagner Middle School on Mountain View Drive in Winterport. For information, call 223-0018.