By Jennifer Weiner

Atria. 376 pp. $26

Jennifer Weiner chafes at the "chick-lit" tag. "It's like if a young woman writes it, then it's chick lit," she told the New York Observer. "We don't care if she's slaying vampires or working as a nanny or living in Philadelphia. It's chick lit, so who cares? You know what we call what men write? Books."

But with three bestsellers and a couple of movie deals, Weiner is too busy to fret much about how the marketing machines are touting her wares, and judging from her sales numbers -- more than 5 million copies of her books in print -- she probably shouldn't.

Still, she has a point. It's demeaning for authors and their readers to be pigeonholed (and even worse to be chicken-holed). Do we have to fit into a certain demographic to read a certain book? Did an immense audience of hermaphrodites make "Middlesex" a bestseller? Besides, with Weiner, I don't think the marketing meisters have gotten the category right. This isn't "chick lit." If anything, it's "hen lit." These characters are no longer hip and single. They've traded their Miatas for minivans and their Wonder Bras for nursing pads.

Sexist labels aside, what matters to readers is whether it's a good story, with three-dimensional characters and a plot that compels us to stay with it. And for the most part, that's what "Goodnight Nobody" delivers. As in her previous novels, Weiner gives us one of her signature zaftig women struggling to find happiness: Kate Klein, a stay-at-home mother with three children. Instead of Philadelphia (where the author and the main characters of her previous novels live), the setting is a Connecticut suburb, where the unpretentious Kate finds herself living among the very pretentious and privileged upper crust, surrounded by seemingly perfect mommies with perfect figures and perfect lives. They view the unkempt Kate with contempt, and she returns the favor: "Sukie and I had been struggling for cordiality ever since the day we'd met, when she'd told me her kids were named Tristan and Isolde, and I'd laughed, thinking she was kidding, and she wasn't."

There is one other significant departure: Instead of a main character obsessed with her size, she is distracted by the murder of one of the perfect mommies. This means the novel will still be found in the "chick lit" section but on a special shelf reserved for "pink mysteries" (the formulaic girl meets boy, girl gets married, girl moves to suburbs, girl reproduces, girl buys minivan, girl finds dead body, girl cracks case). The dead woman, Kitty Cavanaugh, turns out to have led a double life: mommy extraordinaire to the world but ghostwriter to a blond right-wing bigmouth (think Ann Coulter or Laura Ingraham). The list of suspects increases exponentially as we follow Kate deeper into Kitty's past, but solving the crime feels secondary to understanding Kate and the personal and professional choices she has made.

And so, as much as I enjoyed the vivid, spunky writing, I wish Weiner had red-penned the "pink" part (particularly the final few pages, which struck me as preposterous). We don't need Kate to find a dead "Desperate Housewife" in the kitchen with a knife in her back to hold our interest. No matter how much the marketing harpies flocked around Weiner squawking, "Murder sells books: Kill off someone," adding a mystery element to a character-driven novel gives the book an unintended thinness. The unpacking of a murder calls for situations that can't help but feel contrived. Weiner's got a brilliant eye for a particular social stratum, and her readers would have been better served if she had focused on that.

In fact, I would sacrifice the twisty-turny plot if I could read a whole book just of Weiner character sketches and renderings of suburban atmospherics. To wit: "The Cavanaughs had the same house we did, the Montclaire (six bedrooms, five full baths, hardwood floors throughout). The investors in our development were Italian, plenty of the residents were Jewish, and yet the homes all had names that made them sound like members of the British Parliament. Evidently nobody would buy a model called the Lowenthal or the Delguidice, but if it was the Carlisle or the Bettencourt, we'd be lining up with our checkbooks."

In the end, the bigger and more intriguing problem, the one that is never solved, is why a smart, witty woman like Kate Klein would consider staying with a husband whom she no longer loves -- a man who ignores, dismisses and disapproves of her, who doesn't help with their kids and who seems more concerned with the widening of her thighs than the diminishment of her self-worth.

To her credit, Weiner recognizes that the real mysteries -- the ones without tidy "Murder, She Wrote" endings -- are why we marry whom we marry, why we stay with our spouses (and why they stay with us), whether we're raising our kids as well as we should, and why, in the grand scheme of things, any of it matters. These unknowables couldn't be in more competent, funny or empathetic hands than Weiner's.