‘Turn of the century?’ I asked, and he nodded. ‘You were born at the turn of the century – the twentieth century?’ He looked as if he was in his bluff mid-forties, which is a neat trick when you’re lying half-dead in a hospital bed with a machine that goes ‘ping’ at regular intervals. ‘You’re over a hundred years old?’

Nightingale made a wheezing sound that alarmed me for a moment, until I realised that it was laughter.

‘Is this natural?’

He shook his head.

‘Do you know why it’s happening?’

‘Gift horse,’ he whispered. ‘Mouth.’

I couldn’t argue with that. I didn’t want to tire him too much, so I told him about Lesley, the riot and being locked out of the Folly. When I asked him whether Molly could help me track Henry Pyke, he shook his head.

‘Dangerous,’ he said.

‘Has to be done,’ I said. ‘I don’t think he’s going to stop until he’s stopped.’

Slowly, one word at a time, Nightingale told me exactly how it would work – I didn’t like the sound of it one bit. It was a terrible plan, and it still left the question of how to get back into the Folly.

‘Tyburn’s mother,’ said Nightingale.

‘You want her to overrule her daughter?’ I asked. ‘What makes you think she’ll do that?’

‘Pride,’ said Nightingale.

‘You want me to beg?’

‘Not her pride,’ said Nightingale. ‘Yours.’

13 London Bridge

London Bridge

It’s not easy manoeuvring an articulated lorry up the Wapping Wall, so I hired a middle-aged man called Brian to do it. Brian was balding, pot-bellied and foulmouthed. The only thing missing from the stereotype was a Yorkie Bar and a rolled-up copy of the Sun. Still, I hadn’t hired him for his erudition, and he did get us all the way to Mama Thames’s house without any extraneous insurance claims.

We parked up half outside Mama Thames’s block and half outside the Prospect of Whitby. The staff must have thought it was an unexpected delivery because they came tumbling out – I had to tell them it was for a private party, and weirdly they didn’t seem that surprised. I asked Brian to wait, and picking up my crate of samples from the cab, I staggered over to the communal entrance. I put it down and rang the doorbell. This time I was met at the door by the same white lady I’d seen before among Mama Thames’s cronies. She was dressed in a different, but equally nice, twinset and pearls, and carried a small black child on her hip.

‘Why Constable Grant,’ she said. ‘How lovely to see you again.’

‘Let me guess,’ I said. ‘You must be Lea.’