“Nobody wants to be a second wife,” says Pan, the narrator of Sylvia Brownrigg's Morality Tale. “It's like moving into a new house that still has half the previous owner's furniture in it.” Pan works in a stationery store. She is frustrated by her marriage and feels disappointed in her husband, a man so crushed by the demands of work, his ex-wife and two sons that he can work up enthusiasm only for watching television. The marriage has hit a crisis: Pan thinks she has fallen for another man, a chubby envelope salesman who comes to the shop and wows her with his Zen philosophy and Irish eyes. Could this man be “the one”? If so, what about her husband? What about her poor, rootless, irritating stepsons?

The middle-class marriage, complete with stepchildren, a seething former wife and money worries is a fairly ordinary subject for fiction. Indeed, at the outset this looks like the kind of endeavour that makes critics throw up their hands and demand that women novelists write about war and famine instead. For roughly the first quarter of the book, such a critique seems worryingly justified. The narrative moves slowly. It feels somewhat long-winded. The subject is less than earth-shattering.

What lifts it out of mundanity - and beyond - is Brownrigg's subtlety and skill. Her previous book, The Delivery Room, ranged from domestic to political crises, so this is clearly a deliberate narrowing of focus. She presses her nose up closer and closer to this domestic arena, and as she picks the emotions apart the book becomes compelling. Everything feels so cramped. We barely move beyond Pan's condo and workplace and never stray past her point of view, her circling thoughts and exasperated questioning (“Who led you to think I would actually enjoy picking up floor-stuck Cheerios deposited by your adorable offspring?”). Although it is hard to empathise with the object of her passion - a ginger-bearded “Irish Santa Claus” with a creepy line in notelets is hardly everyone's idea of salvation - the emotions feel completely believable. Brownrigg explores the need and repression, hurt and loneliness that lie at the heart of so many marriages. The result feels fresh and true.

Louise Dean also anatomises the messy modern marriage in The Idea of Love, an engaging book set among expats in the south of France. Middle-aged Richard feels disillusioned with his job in pharmaceutical sales and lonely in his loveless marriage to a French woman. Corporate travel allows for frequent infidelity (“with professional women of a certain age panicking all over Europe, he was more than sorted for sex”), but deep down he just wants contact and understanding: love.

Summer comes and the expat high life accelerates into a “spate of parties”, that kicks off with “phones ringing and gravel whirling, kids in pyjamas thrown into the back of the car”. Things rapidly fall apart: flirtations become affairs and boundaries are crossed. “People lied. People stopped talking to each other.” Richard's young teenaged son begins to show worrying signs of mental instability. There is anger, confusion, rehab, recrimination. It is hard to stop turning the pages.

Dean is a prize-winning writer and her prose can be arresting: a Dutch woman's breasts hang “like used teabags in a too-large white bikini top”, an amputee's stump is “wrapped like salami”. However, at times it can feel as if she is dutifully sticking to a self-imposed brief - analysing the “idea of love” from all angles. She certainly covers the bases (sexual, paternal, maternal, familial, erotic, Christian, platonic), but it can come across as forced and also sets up an expectation of resolution that the book does not quite deliver. Nonetheless, there is much to admire. Dean can be funny and caustic. A scene where the expats run wild through the local town before being ejected from a nightclub is dizzy-paced and crazy. They finally ship out “like the UN leaving a warzone, the roundabout weeds trembled as four by fours took it at full speed”. This book may not succeed on all levels, but it fizzes with talent.

Morality Tale by Sylvia Brownrigg
Picador £20 pp224
The Idea of Love by Louise Dean
Fig Tree £16.99 pp274

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