Lots of baby boomers would ruefully endorse the judgement that, "if you can remember the 60s, you weren't really there". David Mitchell, not born until 1969, has no chance of remembering the decade but has decided to re-imagine the 60s in his new novel.

Utopia Avenue concerns an eponymous British psychedelic pop group, emerging from the deepest obscurity in England in 1967. Mitchell starts his narrative with gritty realism, a bit like Trainspotting set to music. Spare, bare realism seems a fitting style: the 60s themselves can provide sufficient colour and movement for anyone. Having been advised that "all his songs were shit, except for the few that were drivel", Mitchell's hero is hustled by a fake doctor and relieved of his rent money. He proceeds to lose his flat and his job in short order, before a providential meeting with a manager of musicians.

Throughout his career, Mitchell has experimented with various angles and means for telling a story, most notably in Cloud Atlas. He sometimes talks about building and fitting together his novels as though composition were a vast jigsaw puzzle. This jigsaw piece is half as long as War and Peace. Nonetheless, in some passages, the new book recalls Mitchell's best, The Thousand Autumns of Jacob de Zoet, even including a stray member of the de Zoet family as one of the characters.

Oddly, Mitchell seemed more at home on an island within Nagasaki harbour in 1799 than he does in 1967 London. Characters and settings are drawn with an uncharacteristically crude touch. To introduce the reader to grunge, Mitchell inserts "the sunken bunker smell of drains" as well as a cellar "as hot, dank and dark as armpits". Australians might not readily forgive the author for including an antipodean boyfriend called Bruce who answers to the nickname Kangaroo, and calls his partner Wombat.

Mitchell's musicians - Griff, Dee, Elf and Jasper - form a quartet, wander around in a van (sadly, named The Beast), listen to their songs on the wireless, squabble, drink, talk, gossip, perform and succeed. Actually recounting what they do is a difficult literary feat. I reckon only two works have taught a reader how it feels to love and live with and through music. One was Peter Shaffer's play Amadeus, the other James Baldwin's noel, Just Above my Head. Shaffer enjoyed a substantial advantage. His play could weave in moments of haunting lyricism from Mozart's works, while Baldwin had to find non-prosaic, prose words to convey the joy of gospel singing.

Mitchell does write, at some length, about the band's instruments, their techniques of composition and the lyrics they come up with. Often, though, those riffs are accounts of mechanics and acoustics rather than of inspiration. Early on the band's approach is labelled - but in a muddled, convoluted manner - as "pavonine", here construed as "magpie-like, subterranean".

Magpies steal from others, boss their mates and pursue anything that glitters. As a role model, the magpie is something an artist might seek to grow out of. One album from the group is classified as acid rock, folk with acid effects, R and B, folk interludes and passages of jazz. Who could make coherent sense from eclecticism taken to that self-parodical degree?

Interweaving encounters with real musicians - among them Bowie, Cohen, Lennon, Joplin and Zappa - might be intended to add ballast to the narrative, but none of the cameo parts does justice to talent. Jasper inhales a few of Diana Ross' "molecules", but her genius does not rub off. Nor does Mitchell fully integrate allusions to his other books, among them "the Cloud Atlas Sextet", "in 4/4, simple enough".

Another quartet with more mundane names (excepting Ringo) who started recording four years earlier remain familiar, but the Beatles would have provided more raw material for a story. Utopia Avenue too often seems too long and too dull. Editing a renowned author with some considerable achievements to his name may have seemed an invidious task, but a tighter, shorter, more dramatic and more ironic novel could have been the result.

In flashes and patches, Mitchell matches his own customarily high standards. A paragraph on how to stick a hook into a maggot is weirdly compelling. The sublimated passion before two girls kiss is conveyed with rare tension and grace. Too often, however, his quartet just talks and talks, then talks some more.

Their adventure together conforms to the picaresque form, but its trajectory is a little too familiar. As agents of ill-fortune, venal Italian police, a touching family bereavement and the usual rocker self-abuse crop up predictably enough. Some real-life contemporaries chose different fates, and happier endings. The Beatles dissolved in acrimonious anti-climax, while the Rolling Stones seem resolved never to finish at all. Why should they?