If a comic novel is to have a vaguely preposterous premise, it helps if it's one that seems immediately enticing to a high proportion of the readership. And which of us, in a moment of feeling insufficiently cherished, harassed by pedestrian responsibilities and bewildered by the world's demands, has not felt that the most sensible option would be to take to our bed?

We might not take matters as far as Eva Beaver, a librarian from Leicester who dispatches her husband Brian to deliver their twin children Brian Junior and Brianne to Leeds University, throws tomato soup over a chair that she's spent two years embroidering and then trots upstairs to the comfort of her crisp white sheets. We mightn't, for example, consider that our self-imposed withdrawal from the world also included trips to the bathroom, leaving us in the delicate position of imploring friends and family to dispose of our bodily waste in giant freezer bags.

But Eva, it quickly becomes apparent, envisages a radical rethink of her entire life, a dismantling of not only its immediate domestic structures but a reappraisal of the 50 years that have brought her to this point; in the bedroom that she arranges to have stripped of all unnecessary fixtures and fittings, and to have its every remaining surface painted luminous white, she interrogates her memories and beliefs, attempting to free her thoughts from the received ideas and assumptions that have, it now appears, ensnared her.

Predictably, a wife and mother isn't allowed to hide in plain sight without meeting some fairly fierce opposition. Who will cook Brian's dinners, or iron his shirts, or creosote the new fence? Who will keep remote tabs on their twins, mathematical prodigies whose asocial tendencies mean that they are unlikely to slip easily into the swim of college life? Completing the family tableau are Eva's mother Ruby and her mother-in-law Yvonne, neither of them particularly reliable sources of support; and Eva soon finds herself confronted with a mixture of outrage and puzzled disbelief.

Just as her life empties of routine tasks and interactions, it also thickens unexpectedly. Brian's eight-year affair with one of his astronomer colleagues, Titania Noble-Forester, is suddenly revealed, and the pair set up an alternative household in his elaborately appointed shed complex, the better to indulge their shared appreciation of the night skies and Benny Hill. Brian Junior and Brianne fall into the clutches of Poppy, a predatory serial fantasist who inveigles her way into the Beaver household by pretending that her parents have crashed their light aircraft into the white cliffs of Dover and now hover between life and death. And, in a rather more welcome but equally complicated development, Eva meets Alexander, a dreadlocked painter and odd-job man who turned his back on a career as a "wanker banker" after writing off a high-performance car and killing his wife in the process.

With a teeming cast (and there are several more characters who come and go with a certain randomness) and an inviolable organising principle  Eva will not leave her bed, come what may  Townsend was unlikely to run short of comic opportunities. There is much here that her fans will recognise from Adrian Mole's various diaries and from her other books, which include flights of fancy involving lightly fictionalised politicians and the royal family: her perfectly pitched sense of the pathos and absurdity of suburban life; the way that she sends up her misfits and malcontents while simultaneously displaying great tenderness towards them; her understanding of the defences that people build to keep what threatens to overwhelm them at bay.

Townsend's fiction has often hinted at a darkness beneath the humour, but this novel gives it freer rein than previously. Eva begins her retreat as a fairly typical fed-up housewife, sick of being over-used and underappreciated, at once liberated and made redundant by the departure of her children, keen to revivify the brain that seems to her like a "poor thing ... huddled in a corner, waiting to be fed". She ends it as a far more radical figure  not quite the messiah that the distressed and needy masses who begin to gather beneath her bedroom window hope for, but a character compelled to dispense with all forms of consolation and comfort while she examines the basis of her life. It is, consequently, an occasionally ragged book, its comic touches dissipated by lingering moments of bleakness. It doesn't seem out of place when Ruby tells her daughter that she occasionally looks forward to death: "I'm tired of living down here since everything went complicated."

Two books hardly make a literary trend, but it's interesting that Ali Smith's most recent novel, There But For The, also featured a protagonist who refused to come out of a bedroom. What unites these vastly different books is how cleverly they both explore the immense power someone who decides to halt their story suddenly acquires, and the unexpected shapes that people make around these human-shaped absences. In Eva Beaver's case, once she's opted for a life lying down, what surprises both us and her is not that she's there, but that we haven't, as it were, all joined her.