‘Call them and tell them we’re on our way,’ said Nightingale.

‘What’s our call sign? I asked.

‘Zulu One,’ he said.

I keyed the microphone. ‘Tango Whiskey One from Zulu One; show us dealing.’

There was a bit of a pause while TW-1 digested this. I wondered if the duty inspector knew who we were.

‘Zulu One from Tango Whiskey One; copy that.’ The Inspector had sounded flat, neutral. She knew who we were, all right. ‘Be advised that the suspects seem to have crossed the river and may now be on the south bank.’

I tried to acknowledge but it came out strangulated when Nightingale put us the wrong way down the one-way system on George Street, which you’re not supposed to do even with your lights and siren on. Not least because of the risk of coming face to face with something heavy and designed to clean streets in the middle of the night. I braced my legs in the footwell as our headlights lit up a two-metre, cherry-red Valentine’s heart in the window of Boots.

TW-3 called in: ‘Be advised that the suspect boat is now on fire, I can see people jumping off.’

Nightingale put his foot down, but mercifully we turned a corner and were back going the right way down the street. On the right was Richmond Bridge, but Nightingale went straight across the mini-roundabout and down the road that ran beside the Thames. We heard TW-1 calling in the London Fire Brigade fire boat – twenty minutes away at least.

Nightingale threw the Jag into a right-hand turn that I hadn’t even noticed and suddenly we were racing through pitch darkness, jolting along a track with gravel pinging off the bottom of the chassis. A sudden turn to the left and we were running right along the water’s edge, following the river as it curved north again. A line of cabin cruisers was moored close to the opposite bank, and beyond them I could see yellow flames – our burning boat. This was no modern pleasure cruiser, it looked more like a half-length narrowboat, the kind owned by homeopathic entrepreneurs that was supposed to have hand-painted gunwales and a cat asleep on the roof. If this boat had a cat, though, I hoped it could swim because it was on fire from stem to stern.

‘There,’ said Nightingale.

I looked ahead and saw figures caught on the fringes of our headlights. I called it into TW-1: ‘Confirm suspects on the south bank near … where the hell are we?’

‘Hammerton’s Ferry,’ said Nightingale and I passed it on.

Nightingale braked the Jag and we pulled up opposite the burning boat. There were torches in the glove compartment, vulcanised monstrosities with old-fashioned filament bulbs. Mine proved reassuringly heavy in the hand when Nightingale and I stepped out into the darkness.