Completed in 1353, The Decameron must be one of the most plundered works in literary history. Some, including Chaucer, Shakespeare and Keats, simply borrowed the odd plot or character from the 100-tale compendium. Many, however, have adopted Boccaccio's idea wholesale.

In the original, seven noble women and three gentlemen flee a plague-ridden Florence for two weeks in a hillside villa. With time off for washing and prayer, 10 days are left for telling stories, many of which involve sex.

Most modern rewritings have attempted to do more than simply provide a new setting in which to assemble their storytellers.

Rana Dasgupta's Tokyo Cancelled (2005) huddled 13 stranded airline passengers around an airport baggage carousel, seemingly to say something about global anonymity and interconnection.
Julia Voznesenskaya's The Women's Decameron (translated from the Russian in 1986) placed 10 women in a Leningrad maternity hospital to anatomise the last days of the Soviet Union.

Most recently, in Ten Days in the Hills (2007), Jane Smiley sent a group of Hollywood types into their mansions in search of refuge from news of the Iraq war. Now, with her 27th novel, The Spa Decameron, it's Fay Weldon's turn to have a go.

A residential spa during Christmas should be the perfect setting for a decameron. Vaguely aware of rumours of Sumatra flu but replete with other problems, a group of "high-achieving" women, known only by their roles as the Mortgage Broker or the Vicar's Ex-Wife, gather to sip Champagne, shed cellulite and tell tales of sexual shenanigans. Tricks, disguises, poison, poltergeists and the high drama and comedy of betrayal and revenge abound.

"But why are you telling us all this?" asks the Surgeon of the Weather Girl who cried rape for £12,000. It's a question we might ask of Weldon and her novelist-narrator Phoebe Fox.

We learn that "high fliers" are unscrupulous and unappealing. That, between men and women, cruelty is a "two-way street". That sex, even with a yob, is good for the "tiny muscles of the face" (it makes you look "softer, a little anxious – more, frankly, female").

That eastern Europeans are rather "quaint", the women wearing embroidered blouses (even in board meetings) and the men resembling "mountain tribesmen" (even while driving taxis). That "men are different from women". Weldon is big on what one character calls "the old common sense".

Mostly the pleasure of the novel comes from its topicality (Skype, no less) and bitchiness. Weldon's women are, as ever, enjoyably cutting about each other's figures, hair and clothes: "She was not fat but she looked fat, like so many people who have only come to a state of slenderness through excessive dieting." It's fun, if repetitive.

Unfortunately, Weldon has ambitions to do more than mock exfoliation. The Castle Spa on its Cumbrian hill is clearly meant to recall the Valley of the Ladies where Boccaccio's ladies go, briefly abandoning the men. The medieval valley is circular and surrounded by six hills, each with a castle-like palace on top. At its centre is a crystal-clear lake, a font of creativity into which the ladies immerse themselves before resuming their tales.

The modern world can only offer a Jacuzzi to Phoebe. But the small scale of the amenities does not prevent her from launching into a full-blown social diagnosis.

About half-way through the novel, the Conspiracy Theorist offers the bath-robed ladies a vision of a world in which an organisation called the Gramsci Project promotes Big Brother, human rights, sperm banks and political correctness in order that society "in its indulged pleasure-seeking state" will destroy itself.

While Phoebe doesn't believe in organised plots, she is ready to think of doom. "You don't go to church on Sunday, you go to a shopping mall instead." From which, it seems, follows, "Islam laughs, China laughs. There are more of them than there are of us."

The ladies spend £5,000 and 10 days in the Cumbrian waters to be made "ready for what happened next". It's a "snip", says Phoebe.

Readers of this novel will spend only £14.99 and the time it takes to read 329 pages. They might be better advised to buy some exfoliant.