She watched the back of her young pupil’s bobbing head, the jug-ears reddening with concentration and exertion, pondering how teaching – like learning – was about so much more than the subject matter, and precisely why she liked it. In Cambridge it would never have occurred to her to give piano lessons. Her piano, an early gift from a godmother and shipped from Amersham soon after she and Lucas got married, had never fitted easily into any of their various homes, ending up always in hallways or behind doors. Even in their final, relatively spacious house, it had lived wedged up against the wall alongside the table in the dining room, which also happened to be directly under Lucas’s study. No matter how pleasant the ‘noise’ drifting up through the floorboards, he explained, after Esther had treated herself one child-free afternoon to a session of rusty playing, it still – regrettably – interfered badly with his concentration. Could she wait until he went out? If she didn’t mind? Not that he wanted to be unsupportive.

Viv had voiced an early theory with regard to her and Brian, that every marriage, no matter how blissful, reached a pivotal moment, when the last vestiges of its original innocence fell away, revealing two very different people glaring at each other, both badly in need of rolling up their sleeves to start the real work required to achieve harmonious, lifelong cohabitation. With them, she said, it was triggered by Brian’s defence of a decision to prioritise finishing an emergency root canal treatment over ensuring getting to the hospital in time for the arrival of their second-born. He had got there just after the birth, not even in time to cut the cord. That it was the wrong call was what mattered, Viv had seethed, making her truly wonder who – what – she had married. He should have downed tools. There had been a perfectly capable colleague on hand. He should have put her, and their child, first.

Between her and Lucas however, it had always felt to Esther as if the very opposite pattern was in play. Their own, hideous, irrevocable tipping point – reached a few weeks before the actual split and still hard to look back on – had been preceded by a million tiny destructive moments, each as imperceptibly corrosive as the drip-drip of water hollowing out rock. It meant that when the crisis came there was nothing for them to fall back on, no resources left on which to draw.

‘I’ve finished, Mrs Shaw.’ Billy was peering at her with a combination of satisfaction and uncertainty, his stout little arms folded across a pale blue school sweatshirt stained with evidence of the day’s meals and activities.