‘It’s some kind of power source,’ she said. ‘Did he build this? If so . . . why?’

‘I don’t know. The night we came, he said he had to hide something, that the police would be coming for him,’ Elliot said.

They continued along the tunnel for another sixty feet, and Harri bristled with nervous energy that intensified with every step. They rounded a bend, and the tunnel stretched ahead about twenty feet or so, but the lights ended abruptly and whatever lay beyond was shrouded in darkness.

‘What’s in there?’ Harri asked.

‘I don’t know,’ Elliot replied. ‘This is as far as I got. He made me wait out here while he went inside.’

They moved forward tentatively. Harri traced the fingers of her right hand along the smooth rock that formed the tunnel walls. Moisture gathered in the lines left by her fingertips, and droplets ran down the wall in her wake. Watching them distracted her from the looming darkness, and the sense Ben Elmys was lurking in there, ready to do her violence. Then, the damp stone was gone, replaced by black air.

‘We need a torch,’ she said, reaching for her phone.

As if in reply, more lights came on, illuminating a chamber the size of a large church. There were many rocky shelves and outcrops in the vaulted space, and the furthest recesses were lost to shadow.

‘Motion sensor,’ Elliot observed, pointing to a device fitted to the wall near the tunnel mouth.

Harri noticed a large television screen positioned on a stone plinth off to their right, and she moved towards it. As she approached, the screen flickered to life. Elliot joined her.

‘Hello, Elliot,’ Ben Elmys said as his image appeared on screen. ‘Harriet. Thank you both for coming.’

Ben did not look like the same man she’d sent to prison. The eleven years he’d spent inside seemed to have left deep marks. His eyes, which had once been so filled with fire, were subdued and thoughtful. His brown hair was flecked grey, and his face was etched with the marks of sorrow. He was still handsome, and if anything, the loss of his manic edge seemed to make him more attractive, more human. He seemed in spirit more like the man Harri had first met and fallen in love with.

‘Is this a video link?’ Elliot asked. He shouted into the cave. ‘This isn’t funny, Ben. Come out. Tell us how to move the rock. You know we’re trapped here.’

Harri felt a rush of panic. The thought hadn’t occurred to her until Elliot spoke, but he was right. There was no way they could move that huge boulder.

‘You still don’t really trust me, do you, Elliot?’ Ben asked on screen. ‘Do you think I’d ever bring you somewhere that wasn’t in your best interest?’

‘Why don’t you come and talk to us properly?’ Harri asked tersely.

‘Harriet. Sweet Harriet. If I was here, I would come to you, but I’m long gone.’