Stupid, she said to herself. That was stupid. It was one of the main rules about walking in London: you don’t make eye contact. It’s a challenge. This time he had backed down, but you only needed one.

Almost without thinking, Frieda took a path that wound off the main road, then back and then off it again. For most people who worked there or drove through it, this was just an ugly and unremarkable part of London, office blocks, flats, a railway cutting. But Frieda was walking along the course of an old river. She had always been drawn to it. Once it had flowed through fields and orchards down to the Thames. It had been a place for people to sit by, to fish in. What would they have thought, men and women sitting on a summer evening, dangling their feet in the water, if they had seen its future? It had become a rubbish dump, a sewer, a ditch clogged with shit and dead animals and everything else that people couldn’t be bothered to do anything with. Finally it had been built over and forgotten about. How could a river be forgotten about? When she walked this way, Frieda always stopped by a grating where you could still hear the river flowing deep below, like an echo of something. And when you had left that behind, you could still walk between the banks rising on either side. Even the occasional street name hinted at the wharves where barges had been unloaded and before that the rises, the grass slopes where people sat and just watched the crystal water flow down into the Thames. That was London. Things built on things built on things built on things, each in their turn forgotten about but each somehow leaving a trace, if only a rush of water heard through a grating.

Was it a curse that the city covered so much of its past, or was it the only way a city could survive? Once she’d had a dream of a London where buildings and bridges and roads were demolished and excavated so that the ancient rivers flowing to the Thames could be opened up to the sky once more. But what would be the point? They were probably happier the way they were, secret, unnoticed, mysterious.