Jennifer. His university sweetheart, his first love. And, he had told me in a moment of either a) drunken candour or b) misjudged humour, the best sex he’d ever had.

Izzy. Sean’s oldest female friend, who had suddenly reappeared in our lives, apparently with a plan to settle down. What was she to him? Freedom, lack of commitment, no kids, no ties. Another chance at youth, another chance to start again.

Rowan. Jennifer. Izzy. We were all intertwined, had been for years. I had worried that we’d been drifting apart as our lives took us in different directions, but in reality it was the opposite – at least for one of them. One of them had got closer to my family than I would ever have wanted.

But which one of them was it? Which one was playing this elaborate game? The more I thought about it, the more sleep eluded me, and at one o’clock I gave up.

Pulling on my thin summer dressing gown, I padded out of our bedroom, marble tiles cool against the soles of my bare feet. I went to Daniel’s room first, opening the door as quietly as I could and waiting for a moment as my eyes adjusted to the darkness. He had turned the air-conditioning unit off, insisting the low, blowing noise would keep him awake. He often didn’t sleep well on the first few nights in a new place anyway – away from his own bed, his own pillow, his own things – but tonight he was fast asleep, curled into the sheet. I moved closer, leaning in until I was above him, close enough to see the rise and fall of his chest in the shadows of his room. I held my breath and stood very still, turning my ear towards him until I could hear slow, steady breathing, hear the breaths in and out . . . in and out.

It was a habit I’d developed when Lucy was a baby, standing over her Moses basket in the middle of one broken night, unable to sleep until I was sure she was OK, listening in the silence, punch-drunk with fatigue, until I was sure I could hear her breaths coming and going. And here I was now, sixteen years later, still doing it with her brother. Still listening. Still checking, even though I knew it was not entirely rational. Daniel was fine – he had been fine when he went to bed, and he would be fine in the morning.

But it was a hard habit to break.

He was still in his pyjamas, despite the heat. I touched my fingertips lightly to his forehead. Satisfied he wasn’t too hot, I closed his door quietly behind me and went across the hall to his sister’s room.

Lucy was awake, her face illuminated by the light from her phone screen. I opened the door a little wider.