In Nora Webster, Colm Toibin has written a companion tale to his acclaimed novel Brooklyn.

The earlier book was the story of a young Irishwoman at the start of the 1950s who, pressured by her mother and sister, leaves smalltown Wexford for New York, and a life behind a shop counter. Only in the final chapters does Eilis Lacey's decision become irrevocable, when her return to Enniscorthy proves not to be a rapprochement with her homeland and family, but a final farewell.

Eilis's experience was common in the mid 20th-century for many in Ireland who had to leave if they were to survive and flourish. Nora Webster is also a tale of survival, this time of another Enniscorthy woman who, as the novel opens in the late 1960s, is recently widowed. A mother of four - two almost grown-up girls, and two sons - Nora had the life Eilis had originally happily envisioned for herself: a job which ceased when she married and had children, and a contented existence played out against the streets and people she had known since childhood.

For Nora, an intelligent, thistly woman in her mid-forties, the protracted and painful death of her husband Maurice destroys all security. Her schoolteacher spouse had given her a new existence, one of wit and intellect, love and easy friendships. As she reflects, everyone liked Maurice, and warmed to his company. The same cannot be said of her.

Abandoned and bereft, Nora plods through the days, looking after her stammering teenage son Donal and his little brother, the winsome Conor, whose undisguised need to be taken care of is endearing.

From the early pages, it is clear that this is not to be a drama, but an account, at almost glacial pace, of grief, and what such wrenching loss feels like. It is also, as with so much of Toibin's work, a study of motherhood, and its complications, misunderstandings and rivalries.

As we learn more about Nora, she emerges as tricky, and not always sympathetic. She can be unpleasant and even devious, as when Donal is placed in a lower class by the priests at his school and she resorts to drastic, almost shocking means, to have this decision revoked.

Even so one cheers to see a woman defend her young in a way few widows would have had the courage to do in those days, or even now, in the face of the chauvinist spite of the church. Confronted by her elder daughter Fiona, who is newly qualified as a teacher and outraged by what she has done, Nora tells her, "I'm lucky that I didn't consult you, then, aren't I?"

Nor is her relationship with Donal perfect, his aunt more affectionate and open and generous with him than his mother can ever be.

What storyline this novel contains is incremental: to raise money, Nora sells the family's rundown summer cottage by the sea, accepts a job in her old office and outwits a manager who tries to control her; she has a haircut, joins a gramophone society, and takes singing lessons. Music, which is her only extravagance, soon becomes her spiritual solace, the thread along which the staging posts of her gradual return to life is strung.

In prose as functional as it can be without feeling abrupt, Toibin unreels Nora's life parsimoniously. He never rushes, never excites. "One Saturday a few weeks later, she went on the train with Fiona and the boys to Dublin. They met Aine in The Country Shop for a late lunch, and then she asked the girls if they would look after their brothers for an hour or so, as she needed to go shopping on her own."

Cups of tea, buying a new dress or redecorating a room - are all given equal weight. The cumulative effect of so much small detail is initially beguiling, but gradually the unremitting restraint of tempo becomes claustrophobic and dull. The exactitude of getting from one place to another is described as if it were a feat of memory, and the tedium of a minor medical complaint given overdue emphasis is justified only by its unexpectedly supernatural side-effect.

This is risky fiction, Toibin daring to be ordinary and downbeat while exploring something as cataclysmic as grief.

One doubts there have been many such careful and precise depictions of a widow's plight, nor indeed of the way a single woman in a restrictive and judgemental society makes her way without losing her sense of self. Toibin is never less than feeling, yet there is no note of sentimentality or cliche. Like all such major loss, Nora's bereavement is as unique as she is, almost as unfathomable to her in the way it unfolds as it is to onlookers.

Toibin's descriptive rigour is only occasionally lifted from the particular to something more profound, as when Nora recalls sitting by with her mother's corpse: "All the natural life had gone and instead something else had come, something a long time in the making. It lingered there, and then it faded and something else replaced it. The face exuded an impression more powerful than anything it had ever done in the days and night when there was breath and voice."

That passage speaks to the whole novel, the author's exercise in acute observation intended to create a character's inner life as real as our own. Whether he has succeeded is another matter.

For this reader, Nora is too emotionally costive and elliptical, her behaviour in some scenes too bafflingly cold, ever to allow her to be fully known or understood or, indeed,

for her story to be completely absorbing.