Playing with the Grown-Ups, By Sophie Dahl

Call it unreasonable, but a "somewhat autobiographical" first novel by a supermodel whose grandfather happened to be a good writer doesn't always fill the heart with joy. Envy, perhaps. Schadenfreude. But not joy. Particularly when the cover glitters with fairies. And the blurb describes a character as a "silver-eyed beauty". This is a shame, because this novel is really not bad. Which obviously doesn't help the envy or the schadenfreude.

Kitty is a young girl growing up in a "somewhat" unconventional family: doting grandparents, two half-siblings and her mother, Marina, "a beauty, a painter and a weeper". It could be classic misery lit – mother ups sticks with "Swami-ji"; mother dumps bookish daughter in vile boarding school; mother returns and has shedloads of sex and drugs with mortified daughter's friends – apart from that Dahl doesn't seem to do misery. The voice of teenaged Kitty, that uncomfortable mix of arrogance and crippling self-loathing, is spot on. But unlike the average teenager she doesn't blame her mother for anything. Instead, she is bewitched by the feckless Marina. It's hard to understand why, without viewing it through real life and Dahl's own mother's manic depression.

Apart from a slightly troubling reliance on her own press cuttings, there are heavy shades of other writers here. The gung-ho eccentricity and the beautiful, selfish mother – a real bolter, this one – reek of Nancy Mitford as if the author has doused herself with The Pursuit of Love as Kitty does with orange blossom and Chanel No 5. But this attitude – very U but totally un-PC – doesn't sit well in modern London. Filtered through arch literary references ("It's all very Brideshead,") and psychobabble ("'I think..."'Kitty said, 'it doesn't really make a difference where [Marina] is, because she always takes herself with her'"), it reads in places like Mitford and Waugh after they've worked through their issues with an understanding therapist.

When she lets go, however, Dahl is really very funny. I love the hopeless parade of Marina's men and boys. One short-lived husband "went off with a woman lion-tamer named Lou with strong-woman thighs". Another loves her more than life itself but lives in America with his wife. I love the stand-up insouciance of the dialogue: "He likes me to wear my school uniform and call him Daddy." "Doesn't that make you feel sick?" "A bit, but then we go to Cartier and I feel better." And any writer who uses the line, "She was in bed wearing a silk peignoir" with a straight face deserves a prize.

Dahl is at her best with this ballsy tragicomedy, which is genuine and touching in parts. She disappoints when she tries to be deep. And in the present-day chapters, Kitty's supportive husband is too, too sick-making. Likewise, we could do without hearing how desperately beautiful the characters are, through teenage spots and suicide attempts. But maybe that's the envy and schadenfreude again.

Bloomsbury £12.99 (285pp) £11.99 (free p&p) from 0870 079 8897