Two painted wooden or metal cabinets stood close to each other, where the stage had been, with their doors open. There was a third one behind them, slightly larger, set close against the back wall. I walked over and looked at the nearest of them. A showcard on the door said: Willer’s famous vanishing cabinet – see if you can detect the false door.

I peered inside, reaching in with my hand. All four of the internal walls were painted matt black, and felt solid and unyielding to the touch. I stepped a little nearer and pressed more firmly, trying to find any weakness, or joint, or part of a wall that felt different from the rest. Before I realized I had found the key, the cabinet wall on the right slid swiftly to one side, marginally narrowing the space inside the cabinet but making extra room in a triangular cavity that had opened up. Any young or slim person could easily be concealed there. From even a short distance away the interior of the cabinet looked exactly as it had before.

The cabinet next to it used a different system for concealing someone. The doors front and back both opened fully, revealing an indisputably vacant space inside. This cabinet was mounted on castors. Photographs showed that the magician could rotate the cabinet for the audience to see through to the other side. He could even walk through it himself to ‘prove’ that there was nowhere for anyone else to be hidden. But the secret here was not a mechanical device. When both doors were fully open the magician, with perfect timing and a trained assistant, could rotate the apparatus swiftly, while the assistant moved nimbly from the concealment of one open door to the next, ending up inside as the doors were closed, ready for a magical production moments later.

Ketty was standing next to me, observing everything I did.

I indicated the slightly larger cabinet, at the back. Its door was closed.

‘May I have a look at this one?’ I said.

‘I can open it and you can inspect it. But don’t touch anything. This one has a self-operating mechanism, which goes suddenly into action. Three years ago a child, brought in by one of the visitors, had an accident. Since then we always have to supervise.’

At that moment the door to the museum opened, admitting a shaft of brilliant sunlight. One of the engineers I had seen earlier was standing there. The welding mask was tipped back above his head.

‘Ketty, a big party of visitors have arrived,’ he said. ‘They would like you to open up the Scrambler and a couple of sideshows.’

She responded immediately.

‘I’ll be right there, Vejo,’ she said, and the welder withdrew. Ketty turned to Spoder and me, looking indecisive. ‘I have to go. You ought to wait outside – I shouldn’t leave anyone alone in here.’

‘We’re just looking around,’ I said.