AN ADVENT CALENDAR.<i> By Shena Mackay</i> .<i> Moyer Bell: 148 pp., $19.95</i>

John is buying chopped meat in his rundown North London neighborhood when Mick, the butcher’s assistant, lands his cleaver on his own finger. In an uproar of blood, towels and hysteria, the finger somehow falls into the meat grinder.

An hour or so later, John’s semi-invalid Uncle Cecil comes to the table with an anticipatory grunt of “lovely grub” and guzzles up the meat sauce despite the odd bits of bone and gristle. Soon the butcher is at the door demanding the return of the finger. The dog ate it, John lies, stricken. Rather than remark on the manifest absence of a dog, the butcher inveighs furiously at the idea of anyone feeding good meat to a pet.

With this beginning, a reader will expect “An Advent Calendar” to be a work of absurdist humor and perhaps--bearing in mind Shena Mackay’s British (Scottish) nationality and the purposeful use of such humor by writers like Joe Orton and Brendan Behan--of social satire as well.

There is social commentary in “Calendar,” but it is something more desolate than satire. The humor is mainly dark, but there is nothing absurdist about the struggling and penniless young family of John, his wife Marguerite and their two children, the decrepit but sweet Uncle Cecil and one or two friends and neighbors.

Absurdity is in the world they try to manage. They themselves are frail and only shakily competent, but their integral humanity is unquestionable even if it has holes in it, like their breakfast toast (the mold spots having been cut out beforehand). They bear a resemblance to Mr. and Mrs. Antrobus in Thornton Wilder’s “The Skin of Our Teeth,” who try to hold out through our planet’s upheavals from the ice age to the present. Mackay’s characters lack Wilder’s soft-edged whimsicality. Their ice is real, though it dazzles unexpectedly and even harbors, like igloo blocks, a sporadic warmth.

The upheaval that Mackay depicts is specifically the changed ethos of Thatcherite and post-Thatcherite Britain, though it could apply to a more generally troubling contemporary world. In the dismal gray London neighborhood, the social fabric has frayed.

A slaughterhouse and a garbage dump stand near Uncle Cecil’s once pleasant, now decayed house. Electric wires dangle from the walls, the dust is an inch thick and the kitchen is so greasy that when Marguerite lights a burner, the whole stove flames up. The plant nursery Cecil used to run is abandoned, its signboard lying “in a black slime of petals, among slug-trailed panes where long worms and roots writhed through fiber pots.”

Two decades of free-enterprise retreat from the concepts and practices of a welfare state have created more than economic hardship in the neighborhood. The social connective tissue has withered; there is a bleak emptiness between one character and the next. Even those bound by love and family find the links straining.

John, a college dropout, desperately wants to support his family but is too absorbed in his private musings and too disconnected from the world around him for steady work. On his first job for a house-cleaning company, he attaches the vacuum hose backward. When it spews out dirt, he berates the outraged client for keeping a filthy house and, in passing, for her prissy clothes.

Marguerite resumes an old affair with Aaron, a veterinarian, after he turns up to examine Uncle Cecil’s sick goat. She loves John and her children; she also loves Aaron, and Aaron loves her. The world around her is too unstructured to help her with a choice. All three are good and endearing people. They try hard, but just as society’s center has collapsed--a sense of the public as well as the private good--their own centers won’t hold.

There is little action in the book; instead, there is lethargic, random activity, like fish swimming in a murky aquarium. While John and Mary struggle to work, keep house, confront and retreat from each other, their neighbors intersect with various degrees of incompetent good will or sheer malevolence.

Particularly malevolent--he is evil, defined in the theological sense as the absence of good--is Eric Turle, a self-indulgent middle-aged poet. He seduces Joy, a passionate teenage misfit. Besotted with poetry--and eventually destined to work in the slaughterhouse--she hides for hours in the school lavatory reading the “Golden Treasury” anthology and ignoring the insistent paging of the public address system.

In his wife’s absences, Eric wins Joy by reading poems and plying her with Camembert. When they manage to spend a night together, she scribbles a love poem, awkward but quite lovely, in the notebook he keeps beside the bed in the event of inspiration. (There has been no such event for years; the pages are blank.) When his outraged wife discovers it, he claims that he has written the poem for her; they both turn on Joy, a heroine though ill-fated.

Another incompetent innocent is Elizabeth, a teacher who tries to befriend Joy and do other bits of good, all of which turn out badly. She impulsively invites a drunken street-cleaner for Christmas dinner, then practices cutting her hand for an excuse to put him off. She harbors an insatiably needy and vindictive school friend, who tries to hang herself from the shower rail and, failing, proposes going out for a drink.

Neither good nor evil is concerted. Just as society has disconnected from the individual, the individuals have disconnected from each other, despite their yearnings, and eventually from themselves. Even the most appealing of them lack the dimension of hope: that is, a sense of the future implicit in their present. One dimension less does not result in flatness but in a poignant evanescence.

Mackay suggests evanescence quite wonderfully with a prose that alights, vanishes, pops up elsewhere, interrupts itself and turns up again with unexpected finds. It can be disconcerting; no sooner do we delight in a person or passage than it breaks off. It is as if the author is keeping a distance from authorship; as if what she provides is something found by chance, undependably and possibly illegally.