His voice was muffled, and because of the noise coming from outside I barely heard what he said. He stepped further forward, one foot balancing his weight inside the cabinet. Then he took a second step and was completely inside.

The music from the Scrambler changed abruptly: a heavy rock number began, with a screaming, insistent lead guitar. A singer yelled out vocals. The shouting and whooping of the people enjoying the thrill of the ride increased by a decibel or two. The racket of their fun was barely diminished by the wooden walls of the museum.

I moved back a little, watching what Spoder was doing. I knew the front screen of the cabinet would be closing again soon, but I did not know how to prevent that. All I could do was re-open it once it had closed.

‘There’s nothing to see here,’ he said. I leaned forward to hear him better. ‘I thought there might be a way of triggering the mechanism. Some hidden pedal, or a switch—’

He had turned around, facing away from me. His hands were reaching up towards the top of the cabinet, where there appeared to be some soft material where the wall met the internal ceiling of the cabinet. I saw him pressing against it.

The front of the cabinet closed silently. There was a sudden thud, and I sensed a heavy movement as well. I grabbed the key, thrust it into the lock. The cabinet opened again. In the space of two or three seconds Spoder had disappeared.

In the indirect light at the back of the museum the black-painted inside walls of the cabinet gave away no details. I knelt down and reached forward, groping for some clue as to what had happened. This cabinet was slightly more spacious than the one I had investigated a few minutes earlier, but felt just as solidly, unshakably built.

‘Spoder?’ I shouted, feeling foolish because I was certain he must be concealed somewhere behind a false, movable wall. ‘Where are you?’

I heard a voice, but with the music still throbbing in from outside I couldn’t make out what he said.

‘Say again!’ I shouted.

‘Down here, sir!’ I heard him gasping. ‘It was a trapdoor – I fell through. I’ve hurt my leg, my ankle. I’m in the dark – let me out!’

He started banging on the base of the cabinet, from below.

‘I can’t see how to open it!’ I said loudly.

‘There’s no air down here. It’s as hot as an oven. I’m having to crouch and I can hardly move my arms.’

‘The trapdoor must slide,’ I said. ‘Try moving it to one side.’

‘Which side?’