Douglas scratched his grizzled cheek thoughtfully. ‘Fair enough. But it sounds like you put a grenade under them today. Let’s give them time to respond before you go in half-cocked.’

In the early evening, when the worst of the heat had dissipated, Nash was sprawled on the top bunk in a pair of shorts when there was a knock on his door. It was Sura, freshly showered, in a pink T-shirt, denim shorts and sandals. She was carrying a tablet and two bottles of iced tea.

‘I’m so sorry for what happened earlier, Mr Nash.’ Her eyes met his. ‘We’ve all been so tense getting here, but it wasn’t fair on you and I apologise. If you feel up to it, could we have that meeting now?’

‘Be glad to.’ Rolling off his bunk, he landed lightly on his feet and took the proffered drink. ‘But why don’t you call me Rob?’

‘OK.’ She smiled prettily. ‘Rob it is.’

They went to the mess, where there was space to spread out. Sura began by showing him recent photos of the Hoosenbeck Gorge on her tablet, and Nash was captivated by the detail, especially the disappearing river at the top of the escarpment.

‘Have you seen anything like this before?’

He shook his head. ‘Rivers in limestone country often flow underground when a sinkhole collapses, but a 1000 metre subterranean drop? It’s mind-boggling.’ Nash paused to stare at the image again. ‘There must be untold marvels inside that cliff face, a whole network of dry and wet caves to explore.’ Looking up, he nodded thoughtfully. ‘The forces involved suggest the cave lake may well be an incredible depth.’

‘How deep?’ Her brown eyes were intense.

‘Well, easily one to two hundred metres, quite possibly more.’

‘And you can go that deep?’

‘Deeper, given the right equipment and resources.’

‘What motivates you to do it, Rob?’

Hand beneath her chin, she stared up at him expectantly. Although it was probably Javanese flattery, it was a question he never tired of answering.

‘I suppose I’m fascinated by hidden worlds. People talk about the ocean as inner space, but for me, an underwater cave is the ultimate expression of it. Not only is it knowing you are the first human being to have ever set foot in a place, it’s the fact you are completely dependent on your planning, equipment and training, which makes it intensely satisfying, sometimes even . . . spiritual . . . to discover what is there.’

‘But cut off beneath the surface in such dark and cruel places?’ She shuddered. ‘I think it would freak me out.’

Feeling the spectre of Natalie rising, Nash drained his iced tea, and wiped the condensation from his hands.

‘So, how long is this film to be, then, Sura?’

‘Oh, I think a one-hour feature – possibly ninety minutes if we get enough footage.’

‘And the angle?’