By Mark Howell

To this humble reviewer, Hy Conrad in his “Home Exchange,” now playing at Waterfront Playhouse, has come up with a whole new genre that can only be called “murder farce” — farce defined as the world turning upside down every time a door is opened and murder defined as, say , unlawful death.

The doors in “Home Exchange” include a front door — when the lock isn’t stuck — and a bathroom/ bedroom door. The murder might or might not involve a corpse buried in the garden or possibly occupying an apartment in New York.

There can be no doubt about the farce but the murders may be another matter. There are sufficient clues by half time to suggest a corpse somewhere … but then those doors open again and everything folds up on itself and you can’t be so sure any more. We do get, however, not to give anything away, a last word on that.

As always when a local stage is designed by Michael Boyer, the set is one of the stars of the show. His “cottage just outside Cambridge, England,” is (I can confirm from medieval experience) picture perfect, complete with mullioned windows just feet away from the cottage next door. Other British details in “Home Exchange” are just as telling; warm ice, for example.

Owners of the Cambridge cottage have swapped their space with apartment dwellers from New York City for a vacation exchange. The theme might remind you of the romantic comedy starring Cameron Diaz and Kate Winslet called“The Holiday,” but “Home Exchange” at the Waterfront is the world premiere of a stage play by Key West resident Hy Conrad, writer/ producer of the Emmy-winning TV series “Monk” and “White Collar.”

The director is Bob Bowersox who’s part of a new theater generation in Key West who has spent the past quarter century in professional film, TV and stage work in Philadelphia and New York. His production here has a most genial and yet distinctly unsettling pace to it.

The American pair whom we see, as opposed to the English couple in Manhattan who are as invisible to us as they are integral to the plot, are brother and sister. He’s gay, she’s single, and both are well wrought by Michael Aaglan and Nicole Nurenberg, the former returning to the Waterfront after “The Best Man” and “Reefer Madness” three years ago and the latter a member of the ace cast of this season’s “August: Osage County,” now undeniably back after a 17-year hiatus from acting.

Their foil is the immediate neighbor, a fellow called Patrick, played to the hilt in very English duds by Brandon Beach, last seen in the electric “Match” at the Red Barn.

The interfering Mrs. Weaver is played by the English-born Joan O’Dowd and her accent is dead on; she’s a kind of den mother to all the characters who surround her.

Last on stage is Constable Greely, appearing in time for Act Two just after the mystery arises of the cat in the locked closet (or not). Performed by Tom Murtha in what must be his 101^st role on the Key West stage, he plays the copper with all the aplomb the part calls for.

There is amateur sleuthing aplenty in “Home Exchange,” along with enough of the bi-polar to pitch it all off the rails. Aaglan and Nurenberg as siblings are quite as nervy and edgy as you’d expect Americans to be when trapped in Cantabrigia Collegiensis during a heat wave.

And Beach as the nosy neighbor indulges in some unnerving pauses, longueurs of language echoed mystifyingly by the other actors on the night we saw it but actually quite appropriate to the mood.

“Home Exchange” is the centerpiece of the Key West Mystery Fest. It’s the first incarnation of a series of events celebrating the world of mystery and detection (noir and otherwise). It runs through May 26.

Tickets at WaterfrontPlayhouse.org or call 294-5015