An arm grabbed me under the armpit and hauled me up in the classic lifesaving position – I heard an annoyed grunt in my ear.

‘Reynolds?’ I gasped.

‘Quiet,’ she hissed.

She was right. Mr Sten Gun could still be standing at the top of the weir, or he might even have come down it – it’s not like I would have heard him. Reynolds was letting us both float back with the current – the better to put distance between us and the gunman.

‘I don’t think he’s following us,’ said Kumar right beside my ear.

‘Jesus Christ.’ I managed to keep it to an outraged hiss.

‘I’m not the one coming back from the dead,’ he said.

‘Can we please not blaspheme,’ said Reynolds.

I remembered the blows to my chest.

‘The vest caught it,’ I said.

Kumar grunted in surprise – the Metvest is supposed to be stab and bullet resistant but I don’t think any officer I know ever believed it.

‘I reckon we’re clear enough for you to use your flashlight, Sergeant,’ said Reynolds.

‘Love to,’ said Kumar. ‘But it’s dead.’

‘Yours is dead as well?’ asked Reynolds. ‘What are the odds of that? What about yours, Peter?’

I didn’t need to check. I asked Kumar if he had any glowsticks.

‘Just the one,’ he said and cracked it, careful to mask the yellow light with his body.

‘You can let go of me,’ I told Reynolds. ‘I can stand on my own two feet.’

Reynolds let me up, my feet skidded on the floor and I had to lean at a forty-five-degree angle just to avoid being swept away. The water was up to my waist. According to Kumar the water was probably a combination of snowmelt and unusually heavy rain in the North London catchment area.

‘How long have we got?’ I asked.

‘Cave systems can fill up very quickly and this is a system that been purposely designed to fill up as fast as possible,’ said Kumar.

‘I don’t think it’s a good idea for us to stay down here,’ I said.

‘You think?’ said Reynolds.

We decided that, mad gunman notwithstanding, we probably couldn’t push our way upstream even if we wanted to.

‘There’ll be street access further down,’ said Kumar. ‘We should let the current wash us along until we reach one.’

I looked at Reynolds, who shrugged.

‘Let’s do it,’ she said.

So Reynolds got behind me and grabbed my shoulders, Kumar got behind her and grabbed hers and on the count of three we all lifted our feet and let the current sweep us down the sewer pipe.