I didn’t run, but I wouldn’t call what I did up those stairs casual either. Behind me Nightingale came up backwards, his cane held at the ready. ‘Get the grenades,’ he said.

I took the grenades from the satchel, Nightingale took one and showed me what to do. My hand was shaking a little and the pin proved harder to pull than I expected – I guess that’s a safety feature on a grenade. Nightingale pulled the pin on his own grenade and gestured down the basement stairs.

‘On the count of three,’ he said. ‘And make sure it goes all the way down to the bottom.’ He counted, and after three we threw the grenades down the stairs and I, stupidly, stood watching it bounce down to the bottom until Nightingale grabbed my arm and dragged me away.

We hadn’t even reached the front door when I heard a double thump beneath our feet. By the time we were out of the house and into the front garden, white smoke was billowing out of the basement.

‘White phosphorus,’ said Nightingale.

A thin scream began from somewhere inside. Not human, but close enough.

‘Did you hear that?’ I asked Nightingale.

‘No,’ he said. ‘And neither did you.’

Concerned neighbours rushed out to see what was happening to their property values, but Nightingale showed them his warrant card. ‘Don’t worry; we made sure nobody was inside,’ he said. ‘Lucky we were passing, really.’

The first fire engine pulled up less then three minutes later and we were hustled away from the house. The Fire Brigade recognise only two kinds of people at a fire, victims and obstacles, and if you don’t want to be either it’s best to stay back.

Frank Caffrey arrived on the scene, and exchanged nods with Nightingale before striding over to the leading fireman to get briefed. Nightingale didn’t have to explain how it would go down; once the fire was out, Frank, as Fire Investigation Officer, would examine the scene and declare that it was caused by something plausible and sanitise any evidence to the contrary. No doubt there were equally discreet arrangements for dealing with the remains of the bodies in the basement, and the whole thing would pass off as just another daytime house fire. Probably an electrical fault, lucky no one was in there at the time, makes you think about getting a smoke detector, doesn’t it?

And that, ladies and gentlemen, is how we deal with vampires in old London Town.

*

It’s hard to describe what success felt like. Even before I managed to produce my first spell I slowly became aware that I was getting closer. Like a car engine turning over on a cold morning, I could sense something catching on my thoughts. An hour into my practice I stopped, took a deep breath and opened my hand.