You were struck, as you often are these days, by how little, if anything, the children would remember of this. The baby nothing at all, and even the boy almost nothing, unless it became a family story. Remember the time we stayed with your cousins in Yorkshire and a barn owl swooped down on us in the day? And yet, you thought, it must all be there, somewhere, however inaccessible it later would be.

Your husband lowered and raised the window: a sudden blast of cold air, the buffeting roar in your ears. He was white-faced with tiredness and you felt with a deep rush your love for him. You unwrapped a chocolate coin, plunder from your son’s Christmas stocking, and put it in his mouth, then one for yourself, the cheap, grainy, metallic taste of it, and you forced yourself to sit up straight, to stay awake, to keep your own eyes focused, through the hypnotic swirls of snowflakes, as if the strength of your attention might keep you all safe on the road.

The closer you get to home, the slower the roads are, the last couple of miles done at a crawl. There is no snow in London, just the dank residue of slush against the kerbs. Bin bags and cardboard boxes piled up on the pavements, already the occasional yellowing Christmas tree. Through Poplar and the East India Docks. Limehouse and Stepney on the Commercial Road, once Orchard Lane, then a 140brickfield; earlier than that, a series of the East End’s deepest plague pits. Public houses and stables, market gardens and music halls. The Blitz. A scrappy park frequented by local alcoholics and flocks of belligerent pigeons, named after a young Sylheti clothing worker stabbed to death. Syringes among the ancient, weathered slabs of gravestone in the corner by the takeaway’s extractor fans.

Home, you think; a Zeno’s paradox. Motion is impossible and change an illusion. The arrow is neither moving to where it is, nor where it is not, and therefore St Sebastian never died. Zeno of Elea, Plato and his cave, Aristotle, Socrates with his cup of hemlock. The years you spent studying them, trying to shape your mind to think like them. Lately, all they said seems meaningless, or at least irrelevant. Now you wonder if they ever gazed at a newborn’s face and felt the world tilt and fall away; watched a child grow up and felt the panic of time. Motion is not impossible: in fact the opposite. Life rushes by, streams through the attempt to snatch at it, then suddenly parts to show you glimpses of the next world, and the next, the ceaseless change to come.