The Peculiar Memories of Thomas Penman by Bruce Robinson (Bloomsbury, pounds 14.99)

As Sue Townsend has shown, 13-year-old boys make rich comic heroes, their particular blend of intensity, naivety and dirty-mindedness endearing them to adults and children alike. Yet not even Adrian Mole at his most misunderstood suffers such humiliations as Thomas Penman, in Bruce Robinson's novel.

Thomas's problems begin at home, among a family so eccentric that they make Nancy Mitford's Radletts seem like the Waltons. His grandfather, a First World War veteran whose life was saved by maggots, is obsessed with pornography - writing it, collecting it and, in his youth, even posing for it. His father, who permanently sports a surgical collar, is a vile man of violently right-wing tendencies who spends his evenings watching television and massaging the Doberman's testicles. His mother replaces priceless antiques by charmless reproductions. Only his grandmother and sister, shadowy presences in both house and novel, are relatively normal. Small wonder that, like the young Salvador Dali, Thomas makes his presence felt in the only way he can: by leaving parcels of excrement hidden in the furniture.

Thomas is endlessly inquisitive - the most dangerous characteristic for an adolescent surrounded by repressive adults. He shares this tendency with two friends: the first, Maurice Potts, descends to depths of depravity accessible only to a rebellious vicar's son (a favourite hobby being to dig up the graves in his father's cemetery); the second, Gwendolin Hackett, is a gorgeous classmate whom Thomas idolises. Their first date sees him as much at the mercy of his clumsiness as his hormones, but she soon gives him the benefit of her considerably greater experience.

Robinson portrays Thomas's misadventures in some gloriously comic scenes, such as the mayhem that results from Thomas placing coins on his supposedly dead grandfather's eyes and from his confusion of enema and anaemia. He is less successful at creating a sustained narrative or unifying theme: the climactic revelation of Thomas's parentage is both too conventional and too small to focus the energies of the book.

Likewise, flashes of imagistic brilliance, such as the vicar with a cough "like one of those unfortunate dogs who've had their bark surgically removed", sit alongside passages of sheer incoherence, such as "If the train was late, and this morning it was, Rob would get on the wristwatch". Inconsistencies (when Thomas is clearly 13, Maurice is described as "six months older, nearly sixteen") and lacunae (it is never explained how a cockney family acquired such a well-stocked Broadstairs mansion) underline an insufficiently realised fictional world.

Robinson is, of course, a highly successful screenwriter. In time, Thomas might well find himself living in Camden Town squalor with Withnail or even with "I". It is as if he has brought all his expertise at orchestrating brilliantly farcical set-pieces to this, his first novel, while neglecting the equally important bits in between.

Michael Arditti