I ran up the steps of the barrack block in some trepidation, but again I was in luck. The guys had eaten supper early and gone out again to run a night exercise. Only the two scalies were in residence. I had a word with them, and said I’d be back later. Then it was just a matter of collecting basic essentials from the caving kit: wire ladder, head-torch and bolt cutters, plus a towel, sweater and spare padlocks from my own locker.

In fifteen minutes we were heading back into town, down the all-too-familiar Shosse Entusiastov, past the scene of the fatal ambush. As we went by, I twisted to my left in an attempt to pinpoint the spot. Yes – there was the wooden hut the Mafia had used as a decoy GAI station.

Going against the flow of traffic, we reached the centre of Moscow in thirty-five minutes. Sergei must have been curious about what I was doing, but he had the sense or the good manners not to enquire. I asked him to head for Sofieskaya Quay, and got him to drop me a hundred metres short of the churchyard gateway, at a point where an alleyway ran back between two houses.

‘Half an hour, back here,’ I said.

‘Is good.’ He peered at his watch. ‘Now seven-thirty. Back eight o’clock?’

‘Tochno. See you then.’

I was confident he’d return, because so far I’d paid him nothing, and I liked him the more for not having demanded the first instalment of his fee at half-time.

I walked a few steps down the alleyway and waited till I heard the car move off. Then I came back on to the embankment and hurried to the gateway.

Now, early in the evening, lights were on all over the convent building. Scarcely had I entered the yard when two women came walking towards me; but they passed without giving me a look, and a couple of seconds later I was safe in the pitch blackness of the old stable.

The bolt-cutters gave me sickening thoughts of Toad, but they did their work in a trice. I lifted the cover of the shaft, secured the top wires of the caving ladder round the hinges, and threw the rest of it down. Because of the wires, I couldn’t close the cover while I was underground, but that was a risk I had to take.

Down in the tunnel the smell was exactly as I remembered it: damp, slime, decay. Of course I was scared – but in my experience the best way to hold fear at bay is to keep moving, so I hurried forward towards the river, anxious to discover if the water level was up or down. It was up. It was within three or four inches of the arched roof. Jesus! I should have brought a mask and dry-suit.