Somewhere close by something was beeping and clanking. A steel container was rumbling down a gantry with a spooky smooth movement. The jaws of the machine released the container onto a tarry barge, then with a whirr slid back up again. No human was anywhere in sight, only this big dangerous piece of machinery with a life of its own. But somewhere in that featureless building people were controlling it: the inheritors of Wiseman’s trade, getting stuff into and out of boats as they had done for hundreds of years.

It was here, I told myself, trying to whip up a frisson. He was right here, sweating with fear. Right here.

I went back to where the walkway crossed the last courtyard, looking for a way to get down to the river, and saw a tall iron gate, conveniently ajar and, on the other side of it, steps going down to the shore.

Stepping through the gate took me into another place altogether. In front of me was a shore of dark grit, stones, glistening slime, then the turbid water of the river. A sudden fresh wind blew against my face. The air-conditioning noises, the traffic noises, dropped away.

The wind funnelling along the river reminded me that, underneath the streets and sewers and polite squares of grass, an earlier place was buried. London was once a wild estuary, gulls crying overhead, wading birds thrusting their long beaks into the mud, and the wind, the constant wind flattening the beds of reeds, the stunted marshy shrubs on the shore. A great pewter sky would have hung like a bowl over the eternal flatness of it, the grey water meeting the grey sky, and at low tide the sheen of cold mud would have framed the metallic water.

The current scoured downstream: fast, hard, dangerous, coursing away towards the sea. Under this lowering sky, the Thames was not benign or pretty. It was a brown and murky river, visibly ferocious. Its teeth tore around the bridge piers, bulging and splitting into white against the stone. Big iron buoys moored in the middle of the stream bobbed against their chains as the water surged around them. The Thames was no toy. The Thames could kill you without even trying.

Boats churned up and down: dragonfly-quick launches, low-slung barges throbbing away against the current making the buoys dance in their wake. There were cruisers, half-cabin boats, Water Police, Metropolitan something-or-other, and now and then a speedy powerboat bouncing along the rough water. Tourist boats with unintelligible syllables of commentary coming at me in snatches on the breeze, people stiff with chill staring at the river, at the woman standing at Three Cranes Walk trying to think about her great-great-great grandfather.

A duck nipped past me, bobbing along on the tide, swivelling its head to look at me, its round eye unblinking.

Beside the steps was a pile of stuff washed up against the wall—rounded brown pebbles, shiny black ones, dark twisted lumps of what looked like coarse glass with bits of sand and stone melted into it. Glass from the Blitz? Another layer of history, all those images of London burning?