He felt faintly ridiculous as soon as he said it. He could see from the expression on Lowther’s face that the man had plenty to worry about. Real or imagined, it was all there in his eyes and in the twist of his mouth. Fear, verging on panic.

‘You’re quite safe, Mr Lowther. I’m here to help you.’

Trying to inject a calmness into his voice that he didn’t feel himself, Cooper spread his hands in a reassuring gesture. His fingers touched the edge of the parapet, and he saw the stone was yellow with encrusted lichen.

‘Is there a dog here somewhere?’ said Lowther.

Cooper smiled then. Bizarrely, it sounded like progress. ‘You recognize me, don’t you, sir? You remember me? I’m DC Cooper. We talked yesterday. I was with a colleague, and you told us about your neighbour’s Alsatian.’

‘Tyrannosaurus.’

‘And we showed you a wooden dinosaur, that’s right.’

‘You don’t have to believe what they’re saying.’

A gust of wind brought the sound of children’s voices up the valley from Gulliver’s Kingdom. Laughter and screams. Kids hurtling over the switchback, plunging into the log flume, their mouths open, their clothes flying.

Lowther inclined his head. ‘They’re there,’ he said. ‘Not far away now.’

Cooper was concentrating so hard on the other man, tensed for a sudden movement, that he was hardly aware of movements on the edge of his vision, the increasing number of sounds around him. He reminded himself that John Lowther saw the world differently, and was probably already in an entirely abnormal state of mind where he saw things that didn’t exist and heard voices that Cooper couldn’t.

For some reason, Cooper couldn’t stop his thoughts wandering. He remembered thinking about the indoor area at Gulliver’s Kingdom, the place his nieces wanted so much to visit. The Wild West, an ice palace, jungle adventures. It was just there, in the distance, prominent among the trees. He could see it without taking his eyes from Lowther’s. Right now, Cooper could imagine himself in the middle of a Wild West shoot-out, that nerve-jangling moment when two men waited for each other to make the fatal first move. Or maybe that wasn’t it. Perhaps he was in the ice palace. Skating on very thin ice indeed.

‘There’s nothing to worry about, sir,’ he repeated. ‘Let’s just go down to the bottom of the tower, and we can talk. We can talk about whatever you like.’

Lowther shook his head. ‘It’ll soon be Monday,’ he said.

‘Monday?’

Frowning, Cooper found the lines of a song going through his head. An old Boomtown Rats classic.

‘So what don’t you like about Mondays?’

‘Not Mondays,’ said Lowther. ‘Next Monday. The thirty-first of October.’

‘Oh.’