A moment later, Cooper was back in darkness, standing in front of a pocket watch that seemed to float in mid-air. When he moved his head, the time on the watch face changed. The hands flicked from eight minutes before ten o’clock to six minutes past, and then to a quarter past. Disturbingly, the Roman numerals were in the wrong place, too. He wondered if it was symbolic. Look, it’s later than you think.

‘Before you ask, there wasn’t anyone else in here. Did you think the lady might have come in the aquarium to meet someone?’

‘It was a possibility. Was she carrying anything when she came in?’

‘Come to think of it, yes. A carrier bag of some kind.’

‘And did she still have the bag when she went out?’

‘I can’t recall.’

In another hologram, Cooper watched an elephant turn into a pig, then a hippopotamus. Further along the wall, a man metamorphosed into a werewolf, and Dr Jekyll became Mr Hyde. Piped music played in the background, something soothing and a bit New Agey. But it was interrupted by noises from the amusement arcade downstairs: the rattle of coins, the blaring music of the video games. Real life intruded, even into a room full of illusions.

‘And that was it?’

‘Yes, that was it. Then she left.’

‘Back down the stairs?’

‘You have to exit through the amusements, but she didn’t stop in there. She was in a hurry to get out by then.’

‘When she got out on to the street, which way did she go?’

‘I couldn’t tell you.’

‘All right. Did you notice anything unusual about her manner?’

‘No. I got the impression she was killing time. In fact, I’d have said she came in to get out of the rain – except it wasn’t raining that day.’

‘How was she dressed?’

‘Oh, I dunno. A jacket of some kind. Not a coat . . . Like I said, it wasn’t raining, or even particularly cold.’

‘Colour?’

‘Black, I think. And slacks – trousers, you know, not jeans. She wasn’t scruffy.’

‘Oh? Did you get the impression she’d dressed up a bit to come out?’

‘Well, she’d made an effort, definitely.’

‘But not to come here? She was just killing time, right?’

‘She wasn’t looking for anyone in here, I don’t think. She hardly seemed to notice other people, except the children. She looked like a self-contained sort of person. Do you know what I mean?’

‘Yes, I know what you mean. Thank you for your time.’

As he left, Cooper noticed that a view from the camera in the thermal bath was projected on to a screen over the entrance. On a busier day, you could watch from the street as children fed the fish or threw their coins into the water, hoping for good luck.