‘What the fuck were you doing?’

‘Didn’t you hear that?’ Pav asked.

‘I sure did. Did somebody fire a shot?’

‘No, no. That was the main beam in the stable going.’

‘Jesus!’

‘Yeah. The whole roof dropped several inches. Shit rained down all round. We thought the place was falling in on us.’

‘Nobody else heard it?’

‘Don’t think so.’

‘What did you do?’

‘Found an old timber lying at the back and managed to get it under as a prop so the beam couldn’t drop any lower. Then we carried on.’

We’d lost quite a bit of time already, so we made haste to catch up. First we had the laborious task of getting the cases out of the nets, loading them into the rubber bags, then bundling them into the nets again. Experiments with nets full of sandbags, filled to the equivalent weight, had shown us that the best way of shifting our loads in the confined space of the tunnel would be by fitting slings of wide webbing to the nets, fore and aft, and advancing as a pair in line-ahead, one leaning forward and the other back, to levitate the burden between us. It wasn’t easy or comfortable – because the laden net tended to crash into the heels of the person leading and drag the back marker off his feet – but it was better than hauling a huge weight along the floor.

It was obvious that three journeys would be needed, so we set out on the first with me leading, Pavarotti behind, Apple’s section one between us, and Toad carrying his own bergen full of tricks. My plan was that, once we reached the site, we’d leave him there with the first half of the device so that he could start preparing it while we went back for the second.

All went well until we were on the downward slope, leading to the river. Then, as the beam of light from my head-torch danced around in front of me, I sensed that something had changed.

‘Stopping,’ I said.

I slackened off my end of the net and stood still.

‘The water,’ said Pav. ‘It’s gone.’

‘Exactly. I’m sure my marker was just here somewhere. Look – there it is.’ I pointed to the horizontal scratch-mark on the wall.

‘Some bastard’s been in here draining it,’ said Pav incredulously.

‘Can’t have been.’

‘Where’s it gone, then?’

‘You tell me.’

In fact only some of the water had gone. A lot remained. Soon after we’d moved forward again we saw its surface lying still and black ahead of us. As we advanced to the edge of it I realised that even at its deepest point it no longer reached the roof: there was a gap of about a foot under the arched yellow bricks, and I could see right through to the other side.