‘I know,’ I said. ‘Last night I learned that Quin and De Chauncey were working together. Projects with landlords, with the police – he’s just another scumbag.’

If this was news to Pierce, he hid his surprise. ‘It’s more advanced than that, I think. But Tamesis is certainly not what I thought it was. It’s not going to free the city. Anyway, this plume of yours is different. Nothing to do with Quin, or his little app. It’s from another place, a place inside, telling us which way to go. So, which way is that?’

I pointed. There was no need to hunt around for the plume. It had been there all along, over Pierce’s shoulder – over both his shoulders, a curtain of looping, gulping yellow-black tar in the star-pricked sky, jaundiced light flickering where it squatted on the Mile End roofline.

‘That way, huh?’ Pierce said. His enthusiasm dimmed. ‘Across the road, I suppose?’

I nodded.

‘OK then,’ he said, and he turned to fall into step beside me, and we walked south, towards the plume, towards the cemetery park.

The red lights on the cranes crowded over the City gave the western horizon an industrial, petrochemical look, more refinery than business district. Which suited the half-built financial towers well enough – they dug and clawed and pumped as much as they rose and transcended. They were dirty, extractive objects, pummelling more and more value from the land that rooted them, and purifying it into glass and ineffable space.

The smoke indoors was a product of panic attacks, but I had never decided about the plume. Was it a real phenomenon in the world, or a hallucination that existed only in my head? Neither possibility was very comforting, so I had never sought to reach a decision, keeping it to myself and keeping out of its way. Uncertainty was a more desirable state. No action required, no ugly conclusions.

But now Pierce knew about it, and had pushed me into action. The probabilities were collapsing, and the plume appeared to know it. Our path took us directly south, cutting across Mile End Road, but there were no handy pedestrian lights, and I had to divert my attention from the skyline to the speeding evening traffic. Once we reached the other side, I looked again for the smoke, and could not find it. We walked down the side street that led towards the main entrance of the cemetery park, and I kept my eyes on the southern sky, where the plume had been seen last, waiting for it to reassert itself, perhaps with an apologetic cough.

It did not. It was gone. The night sky was rained out, offensively clear, and I could see all of the twenty or thirty stars that London’s glare permits, and a nail-clipping of moon.