Up ahead of me I saw a pale stunted man, his face mauled by some kind of blistered rash, sidle up to a big black man. As I passed I glimpsed the gold watch laid out on the pale man’s palm.

‘What you looking at, man?’ I heard the black man ask.

The man with the rash came back quick as a whip. ‘Seven quid.’

Under the viaduct of the railway, the arched vaults were crammed with piles of stuff: broken toilet-pans, mattress-springs, seatless chairs, car steering-wheels. Everything was worn-out, broken, dirty, unrecognisable as a useful object, compacted into a dense mass: no longer individual items but essence of rubbish.

Yet a man stood there selling things, watching as people picked over the piles, as if they might steal something. Taking money for a handful of rusted nails, giving change out of a leather bag hanging from his belt.

In the romantically named Cygnet Lane—a rubbish-strewn passageway between dark weeping brick walls—worn women in saris held out packets of cigarettes. They were listless, hopeless, their skins chalky, their faces blank. One slumped on a milk crate, the packet of cigarettes dangling from her hand, staring at the gutter, too worn out even to try to make a sale.

Or were the cigarettes a front, a code—were these women prostitutes?

This was nothing picturesque. This was real, grinding, fearful poverty. These back lanes of Spitalfields were a living museum of the world Wiseman would have known, a world in which a handful of rusty nails was a saleable commodity. This—the ugly face of the first generation of migrants clinging to a big city—was teaching me more about Wiseman than any amount of dawdling about on the banks of the Thames picking up pieces of roof tile.

Next day I made another early start and went south of the river instead of north. Wiseman had married in Spitalfields, but according to the Mormons his son had been baptised at the church of St Mary Magdalene in Bermondsey, and the address of the parents was Butler’s Buildings.

I took the Tube to London Bridge and walked down Borough High Street, past cobbled alleyways and courtyards and along the side of the high brick wall of Marshalsea Prison, where Dickens’ father was incarcerated for debt. Right beside that wall was the Southwark Local History Library. I was hoping someone there could locate Butler’s Buildings for me.

They couldn’t, but they found me a copy of an eighteenth-century map and a magnifying glass. Eventually I located Butler’s Buildings, a long thin street with a kink halfway down. The map showed the buildings, too: nineteen houses in an unbroken row down one side of the street, seventeen on the other. On one side of the street, the houses backed straight onto those in the next street over.

Peering at the map, I was starting to smell the Bermondsey of Wiseman’s time. ‘Mr Choubert’s Tannery.’ ‘Mr Pott’s Glue Manufactory.’ ‘White’s Fellmongers.’

How did they breathe?

Putting my A to Z alongside the old map, I worked out that Butler’s Buildings was now a street called Brunswick Court, a five-minute walk from the river.