Books: Transformed by sunlight on the way to St Ives

Louise Doughty sizes up a diffuse portrait of the artist

The Serpentine Cave by Jill Paton Walsh, Doubleday, pounds 12.99

The difference between the plot of a novel and its subject matter is not always visible. In Knowledge of Angels, Jill Paton Walsh wove a seamless combination of the two and was deservedly shortlisted for the Booker. Her new book does not manage the mix quite so well. The themes it explores and the manner by which they are revealed are far enough apart for the stitching to show. It is a divergence that proves at once intriguing and frustrating.

The Serpentine Cave opens with the incapacitation of Stella, an elderly artist felled by a stroke. When she dies, she takes with her the identity of the lover who fathered her only child. Marian is divorced with two grown-up children of her own. Toby works in the City but has been suspended on suspicion of insider dealing; Alice is a lovelorn viola player. Faced with a mystery, a dilapidated house and a mountain of debt, the troubled trio begin to excavate Stella's past.

What follows could have been a straightforward detective story but rapidly turns into something much more diffuse: an exploration of the nature of human desires. The book poses some vital questions. How do we decide what is important to us - and once we have decided, what happens to all the other bits of our lives which must take second place? Stella is initially remembered as a selfish woman who neglected her child for the sake of second-rate art. Marian has duly rebelled and become a chemist who has always put her son and daughter first. Towards the end of the novel, one of them demands: "And didn't you ever think it might be the wrong place to put children?" Each character discovers their true priorities. That is the nature of their inheritance from Stella.

This process of discovery is intellectually interesting but doesn't pull on the heartstrings in the way such a story should. One senses an argument at work. Each of the characters represents a point of view, in a way that often interferes with how the reader might expect them, naturalistically, to behave.

The weakness of the characterisation is particularly apparent in the oddly formal dialogue. This clumsiness occasionally extends to the rest of the prose: "When she recovered enough to explain herself, Toby and Alice received what fragments of this memory she told over for them with considerable interest."

In return, there are some wonderful moments of description and insight. A hospital room is transformed by sunlight which "eclipses...the neon strip lights on the ceiling, overwhelming their chilly accuracy with a rival vision, in which Marian's mother lay under a sheet of pale primrose, her face jaundiced". Later, the setting moves to St Ives, where Marian discovers the history of the artists' colony of which her mother was a part. The tensions between the artists and the local fishing community are evoked with fine detail.

When Marian eventually traces her father he proves to be an odd, sad man. Although he makes only two brief appearances, his character is more convincing and disturbing than some of the larger ones that give the plot its engine. The Serpentine Cave is a bit like a much-loved but dilapidated motor car, providing moments of aesthetic pleasure which don't quite compensate for its inability to fulfill its primary function.