There's a war on. But it's not the one you think. This battle is playing out under the duvets of Stellar Plains, New Jersey, where the women are confronting their husbands and boyfriends with the most powerful weapon they know: the cold shoulder. Nookie's a no-no, kissing's gone missing . . . yes, it's a sex strike. But not in aid of any particular cause. The women have been unknowingly struck by a spell, which takes the form of a cold  you might say frigid  breeze that quells all sexual desire. They don't realise at first what has happened, and can't explain the change to their partners, who are left to skulk in their garden sheds while the town, emotionally speaking, freezes over.

It could almost be a Greek play  but not quite. Meg Wolitzer, a New York novelist specialising in finely observed relationship stories, has used as her jumping-off point Aristophanes' comedy Lysistrata, dating from 411BC, when Athens was bogged down in the Peloponnesian war. Desperate for peace, the Athenian wives, led by Lysistrata herself, take a vow of chastity and persuade the women of Sparta  the enemy  to join them. Cue a lot of singing, dancing and badinage, some performed by men wearing enormous erect phalluses. What could be jollier?

Unfortunately there are no enormous erect phalluses on display in The Uncoupling; it's not that sort of book. Wolitzer maintains the link by having the Stellar Plains high school put on a production of Lysistrata. (It's the choice of the mysterious new drama teacher; could she have an ulterior motive?) In the lead role is Willa Lang, shy and aggrieved, but starting to blossom in the sunshine of her first real relationship with a boy. Willa's parents, Robby and Dory, are both English teachers at the school. As a lively, loving couple who pride themselves on maintaining an energetic sex life well into middle age, they're especially hard hit by the spell, their smugness fading to bafflement, then dismay. Things get so bad that they buy a "Cumfy"  a monstrous yellow consumer product that's half blanket, half two-person bathrobe  and get under it to watch TV. Talk about the death of romance.

Other people react to the spell quite differently. For some, such as Ed and Bev, little changes. He's a hedge-fund manager, she's an overweight careers adviser at the school, and they go from barely talking to not talking at all.

And so we move through Stellar Plains, with half a dozen women getting hit by the spell in turn. This takes a while; each victim's relationship history must be delved into, her partner's reaction explored, their home and lifestyle described, and so on. All this backstory drags the novel down. One young militant tries to follow Lysistrata's example and introduce a political, campaigning angle to her abstinence, but her bandwagon remains unjumped-on.

When I saw that this book was about a female sex strike, I had hoped to work in a few terrible jokes about the tension rising (but not mounting), and so on. In fact the tension stays stock-still. There's no sense of the townspeople collectively hurtling towards a crisis, because neither the men nor the women compare notes until near the end. Instead, this is a thoughtful, rather sombre look at the death of desire, sacrificed on the altar of comfort. There are lots of sharp insights on the generation gap, the pseudo-intimacy generated by the internet, and American high-school life; Wolitzer displays perfect comic timing in her awkward chats between jocular teachers and mortified teens. No doubt there's some truth, too, in her gloomy assessment of western malaise. All we want, it seems, is to be "comfortable in your own skin and in your own bed and on your own land"  which means closing our eyes to problems such as far-off foreign wars and stagnating relationships. It's all a far cry from Lysistrata, with its flirty naked pensioners and hairy-bum jokes. But perhaps the ancient Athenians might have nodded, and stroked their marble beards, and understood.

Robby and Dory Lang are so popular with the students at their suburban New Jersey high school that they pass the "Teacher of the Year" title between them year after year. Their colleagues envy their marriage for its "stability and reciprocity, the lack of sexism, the love and the passion"  but mostly for the passion. Meg Wolitzer spends pages of her ninth novel lovingly emphasising their conviction that, come what may, "Warmly, hotly, tirelessly, in their own bed they would stay." Naturally, they're proved wrong.

The novel opens with a new school term, and with it the arrival of Fran Heller, a fierce and fearless drama teacher who raises eyebrows by announcing that the school play will be Lysistrata, Aristophanes's comedy about women staging a sex strike. As rehearsals begin, so too does "the enchantment": abruptly, completely, the women of Stellar Plains lose their desire for sex, and not even Dory is exempt. It's her shock that strikes the hardest, but the novel's other women are just as vividly and sympathetically drawn. There's Leanne, the beautiful and polygamous (at least until the spell strikes) school psychologist and Bev, the overweight guidance counsellor whose husband cruelly tells her that she's "really let herself go". There's also Dory's daughter, Willa, who undergoes a compelling transformation as she falls in love and lust for the first time.

The enchantment itself, though, is a little hammy  a literal icy wind that whooshes up nightgowns and under bedsheets. We're reminded far too frequently of its taking hold. ("All around Stellar Plains, the same low, hard wind was beginning to blow [...] and it would keep doing that for weeks, making its circuit, taking its time.") It's Lysistrata itself, under Fran's incantatory direction, that's causing this bewitchment, and here's the novel's problem: the idea that literature could cast a literal spell seems far too naive a hope for a novel so attuned to gloomier 21st-century truths, specifically that "the intimacy of reading had been traded in for the rapid absorption of information. And the intimacy of love, well that had often been traded in for something far more public and open." That said, Wolitzer reminds us that desire is often as inexplicable as a magic spell itself, and this goes some way in justifying an otherworldly element in an otherwise wonderfully worldly novel.

While the adults fret about the decline in reading, their adolescent offspring spend hours in Farrest, a virtual online forest where they wander as avatars, occasionally entering desultory conversations with peers. Wolitzer's description of these teenagers' aimless, compulsive online lives is beautifully droll. She's shrewd, too, on how "this whole generation of kids had fully integrated sex into their lives". With the reclamation of the word "slut" so conspicuously under way in recent weeks, there's a neatly topical mention of two girls wearing T-shirts emblazoned with "SLUT 1" and "SLUT 2". They insist it's ironic but when asked to explain exactly how, "neither girl could".

Dory wonders why their kids don't find a real forest instead. "She knew she sounded asinine even as she said this," Wolitzer writes, "but she couldn't stop herself." Later, seeing novels for sale on the street "as if their owners were surrendering them in an act of radical housecleaning for the new century", Dory/Wolitzer reflects: "The changes in reading were all bound up not only with technology but love and sex too, though it was hard to tease it all apart." But isn't "teasing it all apart" essentially the novelist's job description? Dory's asinine plaints are endearing but Wolitzer's evasions are frustrating.

This is a gentle novel, concerned with gentle, good things: how to make love last, find and cherish intimacy, ensure that books matter. That, along with Wolitzer's humane and witty voice, makes it a delight to read. But when order is eventually restored to Stellar Plains and the story winds to its consolatory end, I couldn't help wishing for a little more catastrophe.