Champion Hill, Camberwell, 1922. A mother and daughter, stripped of their menfolk by the Great War, struggle to make ends meet in their genteel villa. Servantless, Mrs Wray keeps up appearances while her daughter Frances confronts the reality of hands-and-knees housework. Reluctantly, they advertise for ‘paying guests’, and are rewarded with Leonard and Lilian Barber, who are young, noisy, sexy and vulgar, with a whiff of the music-hall about them.

This is perfect territory for Sarah Waters. Women reshaping their lives without men, social barriers dismantled through economic necessity, notions of respectability challenged by the world convulsion of the preceding years. It’s a setting in which she can explore the interface between the internal and external lives of her characters with the heightened sense of reality at which she excels.

Frances, once a frequenter of political meetings with an interesting female lover, is now forced by circumstances to engage with tiny economies and household dirt, leaving no time for an intellectual or personal life. She resents the ‘dishonesty’ of the house which has imprisoned her — ‘the scuffs and tears she had patched and disguised; the gap where the long-case clock had stood…the dinner gong, bright with polish, that hadn’t been rung in years’ — but nevertheless washes the hall floor with vinegar, rakes out the ashes of the stove, struggles to render breast of lamb edible, dusts the ‘barleytwist curves of wonky table-legs and the scrolls and lozenges of rough-hewn chairs’ — all the useless, pretentious furniture that belonged to the lost family life. Frances would happily ‘have the damn things carted away’, but her mother — an excellent study of a distressed gentlewoman — cannot let go of the past.

From the moment curvy, colourful Lilian Barber enters the house it’s obvious which way things will go. She slips off her shoes, not wanting to mark the floor so energetically polished by Frances, and her sweet little feet in their fancy stockings leave ‘small damp prints on the wax’. The very next day she takes an extravagant and semi-public morning bath. Mrs Wray is scandalised by the timing and the cost, but Frances pictures ‘that round flesh, crimsoning in the heat’. It will not spoil anything for Waters’s loyal band of readers to reveal that the passionate affair that ensues between landlady and lodger turns both lives inside out. The sex is blazingly described; we expect no less.

Then, alas, the Plot raises its boring head. A murder is committed; an interminable court case ensues. There’s plenty of scope here for an interesting examination of the assumptions about women within the legal process, but Waters seems more concerned with spinning out twists and turns to provide the requisite number of episodes in the event that a TV adaptation might follow.

The Paying Guests is twice as long as it should be. It’s nearly 100 pages longer than The Night Watch, in which Waters entwined the stories of four Londoners during the Blitz without losing pace.There are a number of skilful cameos in The Paying Guests — faded, suspicious Mrs Wray; Mrs Viney, Lilian’s bloated, life-affirming Cockney mother; Len Barber, leering and dissatisfied but somehow still likeable — but there are only two fully developed characters, and neither Frances nor Lilian are interesting enough to be stretched over 563 pages. The first half is a convincing and absorbing immersion in particular lives at a particular time; the second sags like an overloaded washing line.