‘They died out in around 1000 BC, didn’t they?’ Ben asked.

Madison looked surprised.

‘I know a little bit about it,’ he said. ‘Long story.’

‘That’s right. In their heyday they were spread over a huge territory all over Asia. Then bit by bit, for no apparent reason, their civilisation just crumbled into pieces and they disappeared altogether. Another historical mystery. But we do know that Zakara was one of their cities. Before that it may even have belonged to the Helmand Culture, back in the dim and distant days of around 3000 BC.’

‘But where’s the evidence that Alexander ever built a new city on top of the old?’ Ben replied. ‘You said yourself that there aren’t any written records to prove it.’

If Ben was sounding somewhat sceptical, it was for a deliberate reason. It wasn’t that he personally cared one way or another whether Alexander the Great had ever set foot up here on the plateau, or whether Rigby Cahill’s theory was right. But the more he listened to Madison’s passionate account, the more he understood how hard it was going to be to drag her away from this place when morning came and it was time to move on. If somehow he could undermine her conviction with questioning and logic, he might have a higher chance of persuading her.

‘I never said there were no written records,’ Madison fired back, as rock-solid confident of her ground as before. ‘I said there were no verified written records. See, historians are still slowly piecing together the details of the past, as we go on uncovering fresh evidence. It’s the world’s biggest detective job. It takes time, and a lot of what we’ve dug up still hasn’t been catalogued, much less fitted into any kind of bigger picture that the experts can officially agree on. Sometimes bits of key evidence get stashed away half-forgotten and gathering dust in storerooms and archives without having been fully examined, so nobody makes the connection. The same way that priceless old master paintings occasionally pop up in someone’s attic, or a lost music manuscript composed by Bach turns up folded between the pages of an old book. Fluke discoveries happen all the time. Which means that there are always gaps in our knowledge. Those can take years, decades, centuries to fill. Or never.’

Ben smiled. He should have known better than to try to argue with her. ‘Okay,’ he said. ‘So you’re saying that your father made a connection that nobody else had before.’

‘I wasn’t kidding when I told you that Dad could be obsessive. He spent three weeks sifting through heaps of unsorted artefacts in a back room at the state museum in Kabul in the fall of 1978. That was when he found it.’

‘Found what?’