There is a painting of a girl in a simple blue dress, black hair down her back, reading a book ─ or it could be a letter. She is in three-quarter profile, sitting in a wicker chair with a plump cushion behind her, the small table in the foreground bearing an earthenware tea-pot and a pink cup and saucer. The wall behind her is uneven, with a small pattern of ochre dots. It’s called The Convalescent and was painted by Gwen John, one of a series of ten similar studies all with slight differences. In some the girl wears a shawl, or reads a much heavier book, or doesn’t have the tea alongside, or has dishevelled hair. But you can sense the artist’s satisfaction with the final version in which the muddier hues of the dress have settled into clear and unadorned blue, her hair neat, her expression contained and thoughtful. The little tea-service suggests a degree of modest comfort and is far less stark than the empty plate which appears in one of the versions.

The stillness of the girl’s posture draws in the eye, the mood of the painting a delicate blend of vague melancholy and serenity. Wondering who the girl was, what her story could be was the first spark of Romilly. What she definitely is not, I think, is the centre of a large and boisterous family. I simply can’t imagine that just out of the picture, noisy siblings are chattering while other members of the household move in and out of the room. Clearly she’s not rich: she’s an anonymous member of the middle classes. Perhaps because of the painting’s title she seems slightly fragile, even wistful, temporarily withdrawn from the battle of life.

She seemed the perfect counterpoint to the other main protagonist of Romilly, Lady Cynthia Sheradon, whom I first conceived of as a stock Society butterfly when writing Pommeroy, but who, as the story progressed, assumed an inner life of her own rather different from what I’d originally imagined. Despite her pretence of stupidity, there was a great deal of completely undeveloped character there, an instinctive but unexplored recognition that there was more to life than the shallow selfishness she’d always pursued. But it was still only a glimmer. And she was at such an interesting point in her life: the fading beauty now having to face the pain of diminishing allure in the dull backwater of middle age. How would such a feisty lady, accustomed only to adulation, cope with this? Besides which, Cynthia had been such fun to write. I suppose the simple truth is that I just couldn’t let her go.