I shivered as we went down the narrow stairs. It was cold, like descending into a freezer, but I noticed that when I breathed out my breath didn’t mist. I put my hand under my armpit but there was no temperature differential. This wasn’t physical cold, this had to be a type of vestigium. Nightingale paused, shifted his weight and flexed his shoulders like a boxer preparing to fight.

‘Are you feeling this?’ he asked.

‘Yes,’ I whispered. ‘What is it?’

‘Tactus disvitae,’ he said. ‘The smell of anti-life – they must be down here.’

He didn’t say what, and I didn’t ask. We started down the stairs again.

The basement was narrow and well lit, I was surprised to find, by a fluorescent tube that ran half its length. Someone had mounted shelves along one wall and optimistically assembled a workbench underneath. More recently an old mattress had been thrown down on the concrete floor and on that mattress lay two vampires. They looked like tramps, old-fashioned tramps, the kind that dressed up in ragged layers of clothes and growled at you from the shadows. The sensation of cold intensified as Nightingale and I got closer. They looked as if they were asleep, but there were no breathing sounds and none of the fug a sleeping human being would produce in a confined space.

Nightingale handed me a framed family photograph, obviously looted from a living-room mantelpiece, and transferred his cane to his right hand.

‘I need you to do two things,’ he said. ‘I need you to confirm their identities and check them both for a pulse. Can you do that?’

‘What are you going to be doing?’

‘I’m going to cover you,’ he said. ‘In case they wake up.’

I considered this for a moment. ‘Are they likely to wake up?’

‘It’s happened before,’ said Nightingale.

‘How often before?’ I asked.

‘It gets more likely the longer we’re down here,’ said Nightingale.

I crouched down and reached out gingerly to draw back the collar of the closest one’s coat. I was careful not to touch the skin. It was the face of a middle-aged man, white with unnaturally smooth cheeks and pallid lips. I checked him against the photograph, and although the features were the same he bore no true resemblance to the smiling father in the picture. I shifted round to get a look at the second body. This one was female, and her face matched that of the mother. Mercifully Nightingale had chosen a photo without the children in it. I reached out to feel for a pulse and hesitated.

‘Nothing lives on these bodies,’ said Nightingale. ‘Not even bacteria.’

I pressed my fingers against the male’s neck. His skin was physically cool and there was no pulse. The female was the same. I stood up and backed away. ‘Nothing,’ I said.

‘Back upstairs,’ said Nightingale. ‘Quickly now.’