‘It assumes we have accurate foreknowledge of the future, which we don’t. You can only make decisions based on the information you have at the time. We can’t know that any of us will die.’

‘Experience helps you with risk assessment, though. Crossing the street? You’re probably safe. Going into a region of the Congo jungle controlled by warlords? Not so much. And that wasn’t a hypothetical. I did it – and it was a mistake, a terrible one. I hope none of you ever do the same.’

The room fell silent for a moment. Again Cheng spoke first. ‘I have a hypothetical I’d like to put to you, Professor.’

She nodded. ‘Go on.’

‘Suppose you believed you had evidence of a civilisation millennia older than anything currently known. The evidence isn’t yet definitive enough to convince mainstream archaeologists, but you’re certain you’ll confirm it if you’re given the chance to mount an expedition.’

Nina grinned. ‘That sounds familiar.’

‘That was how you found Atlantis, wasn’t it?’ said Madison.

‘Yeah. Extra credit for reading my first book!’

Cheng waited for the laughter to subside. ‘This isn’t about Atlantis, though. What if it was a completely unknown civilisation? The product of an extinct race, related to but separate from humans. A discovery like that would shatter the foundations of almost every religion, especially the Abrahamic ones where the Book of Genesis is regarded as the literal truth.’ The round-faced young man regarded her intently through his glasses. ‘Would you still try to find it?’

Nina became uncomfortable. He was describing, with unnerving accuracy, a situation she had already experienced, and she was still not sure her eventual solution had been the right one. ‘I would have to give that a great deal of thought,’ she said, trying not to sound defensive. ‘It would be possibly the most groundbreaking discovery in archaeological history. But on the other hand, it would be telling over three billion Christians, Jews and Muslims that the entire basis of their belief system is untrue – to say nothing of the non-Abrahamic religions it would impact. And some people get very angry if their beliefs are challenged. Wars have started over less. So in your hypothetical situation, I would be very, very careful about how I revealed what I’d found.’

She watched for any indication that he somehow knew the truth about events fourteen years earlier, but instead he cocked his head quizzically. ‘So you would try to find it?’

Amusement ran around the room, the students enjoying that one of them had caught out a professor. ‘As I said,’ Nina replied, irked, ‘I’d give it a lot of thought. At one time, I would have gone looking for it, yes. Now, I’d be a lot more cautious. Rushing into things gets people killed. And that’s not a hypothetical answer.’