The unnamed protagonist of Jenny Offill’s short novel, Dept. of Speculation, teaches creative writing and is being hassled within her department about when  her next book will appear.

This is not counting her ghost-written account of the US space program for an astronaut who almost but not quite made it into orbit. In Offill’s case, her first and previous work of fiction, Last Things, was published in  1999. That may explain the controlled urgency that marks the structure of the new book. There are 46 chapters at an average of less  than four pages each. All contain a series of taut paragraphs, holding single thoughts and observations, better to give them weight. This economy seems in part to be the character’s way of calming herself as she prepares for the narration of the climax, cum catastrophe, in her marriage.

Although "my plan was never to get married" and her romantic past (occasionally recollected) has to show plenty of boyfriends from whom she has successfully parted, she does marry – to a "famously kind" man from the mid-west whose job is "scoring sound tracks for commercials".

This union and the birth of a loved daughter  only increase her anxiety. She – as we are forced to keep calling her – might be a fictional case study in Scott Stossel’s brilliant book of diagnosis and self-laceration, My Age of Anxiety. In one of the key short passages in Offill’s melancholy, eloquent novel, the narrator confides that "there is still such crookedness in my heart. I had thought loving two people so much would straighten it." But there are no serene uplands to be found except in dreaming. As her agent presciently advises her: "every marriage is jerry-rigged". The consequences of that observation drive the second half of the novel, where the point of view shifts into the third person and she becomes "the wife", "the hurt one".

He – the husband or, as a textbook on adultery delineates his role, "the participating partner" – has begun an affair.

Adultery has been the great theme of realist fiction for nearly two centuries and still it can animate the novel, notwithstanding changes in divorce laws, and in notions of guilt and shame. In the new dispensation, the wife may not put her head on a train track or take poison or be forced to follow her plutocrat spouse into the durance of American City, but she and her husband will have to go and see a counsellor for the regular "Little Theatre of Hurt Feelings".

Raging, she will force a meeting with his lover (it rains), but still cannot suppress wistful remembrance: "they used to send each other letters. The return address was always the same: Dept. of Speculation". Each has kept them, in the apartment that somehow they continue to share.

Offill brings us neither neat conclusions, nor forgiving accommodations. All that is done between the partners in this stage of their marriage will lodge itself in bitter, recriminatory memories. For instance, at one point, "for the first time, she plays the unplayable card, her daughter’s name". In all their exchanges, there was "a low hum like furious weather".

In her mastery of narrative voice, in maintaining a tight structure that nevertheless gives itself room for interpolations – of proverbs, quotations, historical digressions, even the sayings in fortune cookies (a career that the writer considers) – and in the moral and emotional egotism, misunderstanding (goodness as well) that are here dramatised, Offill’s Dept. of Speculation is a triumph on a small scale but in a major key.