NOT many years ago the career of a talented tyro novelist might build typically thus: a first book receives encouraging reviews but scant sales, followed by one or two more books whereby the writer develops his craft. Then on to the 'breakthrough' novel, when the sparks of critical acclaim and a few prizes might finally ignite sales.

Susan Fletcher's first novel, Eve Green, a young girl's account of sinister secrets in the Welsh mountains, demonstrates how these days, this career pattern is turned on its head. Propelled into the limelight after a modest hardback publication in 2004 to win the Whitbread First Novel prize, it was picked for Richard and Judy's summer read and went on to sell a quarter of a million copies in paperback. How must Fletcher have felt, under the weight of everybody's expectations, writing Oystercatchers?

In the event, she has survived remarkably well. There is much that pays homage to the Eve Green template: a watchful female narrator, some of the bleakest settings in the British Isles, a suspenseful tale that roves back and forth in time, brooding over lonely landscapes and dark deeds in rich, lyrical language. But Moira's voice in Oystercatchers is introspective, more elegiac than Eve's, Moira herself a more complex and challenging central character.

It's an unusual story of love and betrayal. Moira Stone is 27, a scientist married to a landscape artist, Ray. Her life is measured out in evening visits to the bedside of her teenage sister Amy, who lies in a coma in a Welsh city hospital following a tumble from a cliff.

Moira blames herself for that fall and recounts her life story to explain her guilt. Moira was raised on the Pembrokeshire coast with its "huge grey water." Two events when she was 11 destroyed her idyll: winning a scholarship to a girls' boarding school; and the birth of a rival for her parents' affections, the sunny sister she spent the next 12 years despising.

Like Candida Clark, Fletcher works that rich vein of poetic prose in which characters' emotions are closely bound up with objects and landscape. Usually this intense interaction works beautifully: "So we wait, Ray and I.

We feel the earth turn"; "I've felt the world darken and the clouds race." Her evocation of place is magnificent. Birds are a common symbol, whether of sadness or a wild uplift of spirit. "A ball of starlings rolls across the sky."

Less successful is her apparent belief that stacking up descriptions of the tiniest domestic detail adds to the narrative. The account of Moira's schooldays, when she distances herself from her family, tends to dreariness and could have been pared down.

Quite as irksome is a tendency to use short staccato sentences that break up sense without obvious compensating effect: "The guesthouse said No vacancies, and no ginger cat sprawled there. Too cold. Or it was dead. Her nose felt pink." Invidious to draw attention to these blemishes perhaps, but the standard of writing is often so high as to make such infelicities stand out.

Despite them, here is a commendably ambitious and disturbing successor to Eve Green.