I was still waiting to join in but at the same time I was fascinated. I had never heard Hawthorne talk so much – certainly not about himself. And it was true what he had just said. When you think about it, just about every murder mystery you read ends with the arrest. You never see the detective giving evidence. And once the killers have been drawn into the legal process, they become quite uninteresting. They disappear.

‘But you are making the world a safer place,’ Matheson insisted.

‘Is that true?’ Hawthorne blinked. ‘As I’ve already said, by the time I arrive, the murder’s been committed. Nobody’s been saved. And more often than not, the killer’s got what he wanted. He’s inherited the money. He’s got rid of his wife. It’s very unlikely he’s going to kill anyone else.’

‘So the work you do . . . it’s just part of a process.’

‘You could say that. You can’t have law without law enforcement. That’s what I do.’

‘But you’re good at it.’

Hawthorne nodded. ‘I think so . . .’

‘Have you met many murderers?’

‘Yes.’

‘And . . . ?’ Matheson waited with a half-smile, wanting more. But there was no more so he moved on. ‘Are all murderers caught?’

‘All the ones I’ve met have been.’

This got a ripple of laughter from the audience.

‘What gives them away?’

‘It could be anything.’ Matheson still wanted more and this time Hawthorne obliged. ‘There’s so much pressure and the stakes are so high that it’s hard to stay in control. There’ll always be a little detail – it could just be a tic – that gives you away. It’s like you’re playing poker and you’ve been dealt a royal flush. Ace, king, queen, jack, ten. It could be worth a million quid. But you’ve got to be a real pro to know how to keep it to yourself and most killers aren’t.’

Out of the corner of my eye I saw Charles le Mesurier nod at that. He was the CEO of Spin-the-wheel, the online gaming company that had sponsored the festival, so it was an analogy he appreciated. His friend or business partner was leaning forward, listening intently. He didn’t seem to be enjoying the talk.

I hadn’t spoken a word for what seemed like a very long time now but Matheson hadn’t finished with Hawthorne. ‘Does it worry you, appearing in a series of books?’ he asked.

‘Not really.’

‘It was your idea.’

‘That’s right.’

‘Why did you want to do it?’

Hawthorne shrugged. ‘I needed the money.’

There was more laughter. If this was a dry run for Edinburgh and Hay, it was clear that Hawthorne was going to be fine. He didn’t need me at all.

‘And was Anthony your first choice of writer?’

‘Let’s just say he was the first one who was available.’