Theresa Rebeck’s new family melodrama, “The Water’s Edge,” now at Second Stage in a production by Will Frears, is the sort of theater that leaves audiences feeling badly used. After sitting through two hours of lukewarm imitation Chekhov, the crowd blinks and finds itself smack in the middle of a grisly potboiler. It’s as if the playwright tried to cure anemia with bloodletting.

“The Water’s Edge” has dramatic problems from the outset, but at first they are more mundane problems. The failed Chekhovian aspirations in the first act are unmistakable: There’s a once-grand, now faded summer house on a lake, where the neurotic family reunites. Helen, a world-weary mother (Kate Burton), lives on the lake in semi-exile with her two eccentric grown children (Austin Lysy and Mamie Gummer). Their long-estranged father, Richard (Tony Goldwyn), reappears with a busty young girlfriend (Katharine Powell) on his arm.The grandiose Richard strolls beneath the trees, waxing poetic about nature and the inexorable pull of his lakeside boyhood home, before coming to the point: After a 17-year absence, he wants his house back.

And so it goes for nearly two acts – dad wants to reconcile with the children, but mom is bitter; boyish, fun dad is inconstant, while rigid mom is reliable. This is well-trodden terrain, and “The Water’s Edge” marches through the expected formula. Richard, played as a smarmy dilettante by Mr. Goldwyn, is shallow, rich, and insufferably vain. Helen, his long-suffering wife, is tough as nails because – as she never tires of pointing out – she’s had to be.The foul-mouthed daughter, Erica, viscerally hates Richard, yet craves his love, while the vague, possibly slowwitted son, Nate, is predictably loyal to mommy.

There are moments in the play when Helen takes on some of the hazy glow of a feminist heroine – when she seems to stand for all those fine women who cleaned up the mess left by their Peter Pan husbands. This point is underscored by the heavyhanded disclosure that long ago, Helen and Richard’s youngest daughter drowned when dad presumably wandered off for an assignation with a sexy neighbor. Helen has overcome all this, and raised two very nice children on her own (with Richard’s monthly checks), giving her a kind of stature. Moreover she’s played by the estimable Ms. Burton, whom audiences instinctively admire. Contrasted with Richard’s fatuous, suspiciously bosomy girlfriend, Helen seems particularly real and good.

Given all this – and the fact that the production is dedicated to Wendy Wasserstein, identified as a “champion of women playwrights” – feminism might be expected to be among the play’s prized values. But no sooner has the decidedly un-girly Erica rebuked dad for thinking she would care about a pair of gold earrings than she starts cooing about how pretty they are and wearing them with her hoodie sweatshirt. Such feminist impulses are slapped down, right through the gruesome last scene, when Helen’s feminist speech sounds like the ravings of a lunatic.

Confused themes aside, the main trouble with “The Water’s Edge” is its inability to build dramatic tension. Too often, the dramatic conflict feels manufactured by the playwright rather than generated by the circumstances. It’s the sort of play where people are forever saying, “I’m going to walk away,” then lingering for no good reason.

This kind of transparent manipulation reaches its apogee in the final aberrant scene when, in the space of five minutes, “The Water’s Edge” goes from Lifetime movie to horror flick. Helen stops guilt-tripping Richard long enough to butcher him in the bathtub, and Nate, who seemed perfectly nice and a little slow, helps dump dad’s body and plots to kill mom, too.

If these disclosures feel abrupt and unearned, they are. The only way to get from the previous play to this one was to dispense entirely with consistency of character. In the blink of an eye, Helen, a Laura Wingfield type, becomes Clytemnestra. Poor, hapless Nate is hastily transformed into Norman Bates.

But a bloody finale can’t fix what’s wrong with “The Water’s Edge.” As the now-diabolical Nate plots to kill his mother, Erica and dad’s girlfriend stand around, wringing their hands and declaring they’ll call the police. Of course they never dial.

Until July 9 (307 W. 43rd Street at Eighth Avenue, 212-246-4422).