Kate Reddy is Bridget with brains, a woman-not a girl-who knows better.

I Don’t Know How She Does It: The Life of Kate Reddy, Working Mother , by Allison Pearson. Alfred A. Knopf, 337 pages, $23.

Bridget Jones has been cloned many times since she landed on these shores in1998.The usual copycat strategy has been to play up her popular appeal: We’ve suffered a blitz of Bridgets, all of them young, cute, ditzy, funny, sexy, sloppy, schmaltzy. Bridget was lite, ditto the wannabes.

But the latest look-alike takes a different tack: A working mother crazed by her double life, Allison Pearson’s Kate Reddy is older, heavier, sleep-deprived, guilty. “When I was younger I wanted to go to bed with other people,” Kate confides, “now that I have two children, my fiercest desire is to go to bed with myself for a whole twelve hours.” She’s Bridget with brains, a woman-not a girl-who’s been disappointed, who knows better, who’s marked by what she knows and yet still wants to make us laugh. Like Bridget, Kate is instantly the reader’s fast friend.

Both characters were born in weekly columns in London newspapers, Bridget in The Independent and Kate in The Daily Telegraph . Once “novelized,” both became immediate best-sellers-though the name Kate Reddy is not on every Brit’s lips the way Bridget Jones was five years ago. Like her predecessor, Kate is bound for the screen (a $2 million deal with Miramax). And the sole engine of success, for both, is the heroine herself: She’s always the hook, in the column, in the novel, in the film.

Thirty-five-year-old Kate Reddy has been married for 13 years to an “ethical architect” named Rich (who isn’t). She’s the mother of Emily, a 5-year-old girl, and Ben, a toddler. She’s worked for a dozen years as a fund manager at an appallingly, comically retrograde City investment firm. Dressed for work, she thinks she looks like this: “Blondish hair, decent legs, in good enough shape not to be pinned for a mother.” (Note the ambivalence-it’s everywhere.) But it’s not her looks that count, it’s her character, which could be summed up as panicked intelligence dueling with bottled-up love.

If she had time to do her job, her intelligence would assert itself calmly and she would shine spectacularly at work, despite the brutish sexism and contempt for maternity exhibited by her male colleagues (“big animal guys at ease in their pinstriped pelts”). Kate’s boss, a swaggering Australian, is the kind of Neanderthal who overrides objections to his demands with remarks like this: “Hey, we don’t do can’t , sweetie. When did we start doing can’t? Can’t is for pussies.” Kate hardly cares. “Chauvinism is the air I breathe,” she explains, “a bracing blend of Gucci Envy and salty gym residue …. [T]he smell stuns you as soon as you enter the City.”

If she had time to be a mother, she would let her maternal love flow. Here she’s returning from a business trip, anguished because she left her children behind: “Their need for me is like the need for water or light; it has a devastating simplicity to it. It doesn’t fit any of the theories about what women are supposed to do with their lives …. Children change your heart; they never wrote that in the books. Sitting here in the front row of Club Class, nursing a large gin, I feel that absurd organ inside my chest, swollen and heavy as a gourd.”

If she had time to be a working mother, perhaps she would also have time for her husband. The plot of I Don’t Know How She Does It (if you can call strung-together episodes a plot) hinges on the question of whether Kate can keep her marriage from breaking down. Because Rich is possessed of “acres of English reasonableness and … invincible kindness,” Kate can get away with neglect that would shrivel a less-generous soul. But it’s clear from the beginning that her husband is about to crack. And there’s also the danger that Kate will have an affair with an American client, Jack Abelhammer(!), a thin, unconvincing subplot. Actually, all the plotting in this novel is weak, and frankly unnecessary. (Perhaps the author felt that more plot-however flimsy-would mean more money from Hollywood.)

Kate does have time (just barely) to cast a cold eye on everyone and everything, not excluding herself. She imagines Jack Abelhammer fleeing from the “sight of [the] Reddy stomach which, after two pregnancies and an emergency cesarean, resembles one of her grandmother’s rice puddings-the top skin puckered over the granular slush beneath.” Her analysis of her nanny problem is typically astute: “Richard thinks that I indulge Paula …. He thinks she’s lazy, moody and shrinks his socks if he asks her to do anything outside her job description. He thinks she has too much power in our house. He’s right. But Rich doesn’t worry about child care the way I worry; men think about child care with their wallets, women feel it in their wombs. Every twist in the relationship with the person minding your young is a tug on the umbilical. Phones may have become cordless, but mothers never will.”

Though Ms. Pearson has walked all the way around the problem Kate faces, she’s far too canny an author to propose global solutions (she does, however, invent a line of sex toys, “All Work and No Play … for the female executive who has everything except time for pleasure”). Her novel won’t tell you a thing about how other women balance professional ambition and raise children at the same time, just as Bridget Jones’s Diary won’t work as a guide to the perils and pleasures of modern romance. This genre is ego-driven, almost necessarily solipsistic. I Don’t Know How She Does It is narrowly about Kate Reddy, and how she will find her own happiness. The book only works if you’re rooting for her.

Bridget Jones was dopey but her creator, Helen Fielding, had the talent to make her irresistible; Kate is clever and Allison Pearson is more than clever-she’s smart, her intelligence at once wide-ranging and penetrating. But smart occupies an uncomfortable middle ground between clever and wise (clever makes for great entertainment, wise for great literature; smart gets great reviews and disappears in a year’s time). You’ll like Kate-you may even admire her-but Bridget’s still the one you’ll love.

Adam Begley is the books editor of The Observer.