I turned and strolled up the road humming the happy tune of the subordinate who knows that whatever shit hits the fan it wouldn’t be him who’d be blamed for turning the bloody thing on.

It’d have been nice to sneak up on Reynolds and give her a shock, but a good rule of thumb is to never startle someone who might be equipped with a loaded firearm. Instead I approached from the front and gave her a wave. The annoyed look on her face – she obviously thought she’d ditched her surveillance – was rewarding enough.

‘Got your sewer gear?’ I asked as she climbed out the car.

‘In the trunk,’ she said. ‘Are we going down again?’

‘You don’t have to,’ I said.

‘Give me five minutes to get ready.’

It might have taken Reynolds five minutes but it took the rest of us about an hour, what with the milling around, strapping stuff on and testing the equipment. This time we’d borrowed the appropriate waist-high orange waders from a surly man from Thames Water. The CO19 boys insisted on retaining their dark blue ballistic vests and helmets as well, which gave them the unfortunate appearance of modern ninjas who’d given up on the whole stealth thing below the waist level. I was wearing a brand-new Metvest but with a high-visibility jacket over the top. I planned to avoid getting shot, through the deployment of peaceful diplomacy and, if that failed, by making sure I stayed back behind the guys with guns. Zach said we’d be better off without the guns, but that’s the thing about armed police. When you need them you generally don’t want to be hanging around waiting for them to arrive.

It was a good plan and like all plans since the dawn of time, this would fail to survive contact with real life.

When we were ready, Seawoll gave us a farewell admonition not to fuck things up any worse than they were already. Then he, Stephanopoulos and Kittredge skived off to a nearby pub to set up a ‘command centre’.

The surly man from Thames Water popped the manhole cover and bid us to help ourselves.

Nightingale went down first, then the officers from CO19. I followed them down with Zach behind me while Lesley and Reynolds brought up the rear. I recognised where we were the moment I got off the ladder. It was the same intersection we’d reached before an unknown assailant with a Sten gun had driven us over the duckboard and tumbling down the weir, and on our way to Olympia and Chelsea’s underground rave. Then it had been a raging torrent. This time it was merely damp and surprisingly fragrant, at least by the standards of London sewers.

Kumar was waiting for us.

‘You just couldn’t stay away,’ I said.

‘It’s warmer down here,’ he said. ‘I’m surprised you came down at all.’