The trouble with reviewing exponential sex farces such as "The Cottage" is that you can't write anything about them without spoiling the fun.

Well, almost nothing. If you go to the Engeman Theater website, you'll see a teaser about a "rollicking farce" that "unfolds when Sylvia Van Kipness decides to expose her love affair to her husband and her lover's wife." Among the few plot details I can add without alerting you, dear reader, to potential spoilers, is that Sylvia does so by telegram. No one's heard of texting (or sexting) in this new play by Sandy Rustin, an American author inspired by Noel Coward's romantic comedies. Set in Roaring '20s England, it's libido that roars loudest.

Sylvia and Beau have been trysting annually at his mother's country cottage for as long as they've been married to other people -- seven years. It's not guilt that moves Sylvia to reveal their affair without first consulting her co-cheater. It's lust. Sylvia thinks the truth will set her and Beau free from the anchors of their wrong-spouse marriages.

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That her husband and his wife become key players in the ensuing complications seems obvious enough. So there's little risk in revealing their subsequent arrival on the scene, a handsomely detailed set by Jonathan Collins, who turns the title abode into a virtual character. These are folks of means and taste -- comfortable without being conspicuous -- down to their fashion statements (personality-revealing costumes by Tristan Raines).

Other revelations about the married foursome would ruin one saucy zinger or another. So we'll limit our comments to acting chops.

As Sylvia, Rachel Pickup is so beautifully blithe -- also the other way around -- that we see her "confession" as free-spirit spontaneity. Henry Clarke as Beau (not to be confused with Jamie Laverdiere as Sylvia's husband, Clarke) evokes the easy humor of a gentleman who's no gentleman, except for his manners. Aforementioned Laverdiere as cuckolded Clarke turns our expectations into a laugh-out-loud in-joke, while Christiane Noll as Beau's wife, Marjorie, can't conceal her sight gag, which makes it all the more delicious. Let's just say that I've never found flatulence as funny as depicted here (Laura Shubert's sound design). Lilly Tobin as Deirdre and Brian Sgambati as Richard/William multiply the unpredictable delirium, directed with impeccable timing by BT McNicholl.

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Despite Sylvia's dud final line, you may ache with laughter.

WHEN | WHERE 8 p.m. Thursday, July 30, and Friday, July 31, 3 and 8 p.m. Saturday, Aug. 1, 2 p.m. Sunday, Aug. 2, through Sept. 6, John W. Engeman Theater at Northport, 250 Main St.

TICKETS $59-$64; 631-261-2900, engemantheater.com