I recognised the voice at the other end as that of Bill Bravington: I’d spoken to him a couple of times already since our deployment, and had no need to fill him in on background.

‘Bill,’ I said, ‘we’ve hit a problem. The Apple site. The approach is blocked by water.’

‘Wait one.’

I imagined him reaching for a notepad.

‘All right,’ he went. ‘Carry on.’

‘We can’t tell if the site itself is flooded. If it is, we’ll need an alternative. But even to recce it we need breathing kits, dry-suits and half-hour tanks. Plus some of those Boat Troop rubber bags for the components. And two big underwater torches. Can you organise all that soonest?’

‘No problem. How many suits?’

‘Two. Correction: three suits and three tanks. Plus rubber bags.’

‘Number?’

‘For three pieces. You know – two big, one small. But we’d better have spare small bags as well. Say half a dozen small.’

‘Got it. Fins?’

‘Sorry?’

‘Will you want fins?’

‘No, thanks. The distance isn’t great enough.’

‘OK.’

‘And Bill – listen. We need this stuff right away.’

‘We’ll get it all to London tonight, for the next Diplomatic Bag.’

People must have pulled their fingers out all along the line, because the kit reached the Embassy on Monday afternoon, less than forty-eight hours after we’d found the water. On Tuesday night Pavarotti and I were back in the tunnel, with the same back-up team on watch above. On a weekday evening there was more traffic along the quay and more pedestrians about, but we made it into the stable undetected, and down below everything was precisely as we’d left it: the marks I’d scraped in the dirt on the floor were still fresh, the surface of the water still one inch below a horizontal line I’d scratched in the slime on the wall.

The discovery of water and the sight of the various falls had led me to change our plan. I reckoned that if we managed to reach our destination on this second recce, we might as well start opening up the site for the CND. My reasons were: first, that the chances of any inspection team coming through the water within the next few days were zero, and second, that even if somebody did come snooping, a hole in the wall wouldn’t in itself excite suspicion as there were plenty of other natural cavities already.

So it was that this time we had jemmies and small picks in a bergen. Having zipped each other into dry-suits over our clothes, we fitted our tanks and breathing kits and waded into the inky water. On our outward trip the water was fairly clear, and our torch beams reached a few feet ahead – enough for us to spot two submerged heaps of rubble before we blundered into them.