A plot built on shifting sands

Joanne Harris has followed the success of her "food" trilogy, Chocolat, Blackberry Wine and Five Quarters of the Orange, with an indigestible, unappetising and sometimes even tasteless offering. There's the odd food reference to cheer it up - one comfy old lady continually nibbles at candied cherries and someone else menacingly fillets a mackerel - but for the most part Coastliners feels like Chocolat without the chocolate. Which is just about nothing.

It's set in the same French never-never land as Harris's previous books, a nostalgic demi-paradise which makes Peter Mayle look gritty. Harris is half-French and a former modern languages teacher, roots betrayed by mildly ostentatious phrases like "a few flat-bottomed boats or platts had been dragged up the ètier".

Coastliners opens with the free-spirited Mado returning to the small Breton island where she was raised to look after her gruff fisherman father, GrosJean. The island is split into two warring communities - the Houssins, from the flourishing seaside resort on one side, and the Salannais, from the less prosperous end of town, where Mado and her father live. Dismayed by their poverty, Mado and a mysterious stranger called Flynn build a huge reef which they hope will divert the tide and bring sand, and money, back from the Houssins' beach to their own. Of course, things are fishier than they seem, and while shifting the island's balance of power, Mado also uncovers some long-buried secrets and juicy tragedies.

But Coastliners is decidedly short on thrills, especially for a novel so clearly destined for the big screen (Harris knocked out the screenplay in nine days directly after finishing the manuscript). The nail-biting climax involves the distinctly low drama of someone being stung by a jellyfish.

Harris may have been right about food being the new sex, but it's hard to see tidal fluctuations following suit.

Her style is typically faux-sensitive, any potential poetry being crushed by complacency - "luck is like a pendulum, swinging slowly across the decades, bringing the inevitable in its shadow". Her powers of description can falter too: the sea has "a weedy, fishy smell". Dylan Thomas she ain't.

There is also a quaintly moralistic People's Friend strain at work: unwed mothers are humbled, wives with nannies are punished, and when Flynn puts his arms around Mado, she responds "like a flower to the sun".

But the main problem is the people. There are no stand-out characters, nothing for Judi Dench to really get her teeth into. The islanders' feuding doesn't seem important, just petulant. They are self-serving snobs, backbiting without being amusingly bitchy. The aptly named Mado just seems a bit loopy, a fusspot outstaying her welcome, rather than a breath of fresh air.

When the film is released, much will rest on the role of GrosJean, and maybe someone like John Hurt or Michael Gambon will be able to carry it off. But it's a tricky one - he's a deeply unfriendly mute recluse who never shows his daughter affection, lavishes it on his spoilt grandchildren, and is still supposed to charm our socks off. He'd be the dead spit of old man Steptoe if he was more chatty. At one point Mado thinks she may have heard him make a sound, "a long, torn, moaning noise, but that might have been the wind". Or it might have been the readers.