Desert islands have long drawn writers to their shores, but Nicola Barker is not a fan of palm trees and sandy beaches. Rather, she is more interested in mapping her own quintessentially English archipelagos over the course of a series of increasingly eccentric novels and shorter works.

Her latest is a jauntily twisted Treasure Island, and sees the return of Wesley, the hypnotically grubby character who first ambled into life in her short story collection Heading Inland. A maverick environmentalist, serial seducer of librarians and accidental murderer, Wesley has become something of a cult figure, and is stalked by the "Behindlings", a gaggle of oddball obsessives who hobble everywhere in his wake. He pops up here on the estuary island of Canvey, having masterminded "the Loiter", a grand treasure hunt funded by a confectionery company.

The place Defoe once called Candy Island is drab enough but, inevitably, dark currents flow beyond its bungalows and the Wimpy restaurant: man-shaped doughnuts oozing red jam are a speciality here, and the graffiti accusing a local girl of aborting her own father's child is somehow preserved by the salty air.

Although the Loiter provides the novel with its basic plot, it is embellished with baroque and bafflingly unconnected sub-plots, drawing in big business, shady "sugar men" and personal histories of love and hate. Most irritating of all, with a little bit of help from Roget's, Barker achieves a seamless synthesis of form and subject; her prose loiters, circling a single action for paragraphs at a time. The slightest gesture is dissected, parenthetically, while a person doing absolutely nothing becomes "still as an old egret in a fertile rice paddy; rigid as a doubting nun at her thrice-nightly prayers; quiet as a dishonest clerk creeping around after hours; firm as Gibraltar - and just as imperturbable".

In the space of just a couple of pages, Barker is capable of hauling in everything from the Spanish Armada to bathrobes and brass doorknobs. Sometimes it works well, but more often it doesn't: a man shouting out "with all the uninhibited joy of a miserly man who unexpectedly finds his long-lost gold cap tucked inside a three-week-old carton of pasta salad" does not quite seem worth the effort, while her description of Wesley's clothes as smelling "like juniper and off-milk and pipe-smoke-tangerine-old-pelt-grandfather" leaves one feeling that Barker has missed her calling as a quaffer of vins fins.

Naturally, as all Behindlings know, precision is vital when it comes to solving Wesley's riddling clues and winning the Loiter; but eventually, descriptions such as "light/heavy/mad with tension" seem a little bit, well, lazy. When Barker does opt for a single description, it is too often hackneyed, or plain cute: smiles falter, someone is "not a happy bunny", and thought processes are enlivened with cartoonish interjections plucked straight from lips in The Simpsons.

Bafflingly, this is being touted as Barker's breakthrough commercial novel, but even though it certainly isn't as dark as past tales (the pain and blood and mud never quite triumph over the farcical), I suspect that all but the most devoted of her own behindlings will find themselves flagging. This is a shame, because, in the few places where she allows her characters space to breathe, they really do - and speak and think and live.