‘Thanks. I’ll try not to.’

They turned their torches off when they felt they were getting near where Elder had parked. Cooper tried to picture how the site had looked during daylight, orientating himself by the position of the main engine house, looming above him on its high mound. The top of the building, where the roof should have been, was high enough to be clear of the densest layer of fog. He could just make out the upper stonework, jagged and grey. The wheel of the winding gear appeared briefly in front of it, a steel cable glinting and dripping with moisture.

Just ahead were some abandoned pieces of machinery slowly rusting in the damp air. He remembered a small winching truck, its sides eaten away by corrosion, its tyres flat and sinking into the ground. There were iron hoppers and a huge cylindrical boiler, gradually being reduced to such a fragile state of ruin that they would crumble in the fingers.

‘Go carefully,’ said Cooper.

‘I already am.’

The far west of the site had contained the crushing circle and the washing floor. Here, heaps of crushed stone had been dumped, creating mountains of spoil that sheltered the mine from the adjoining fields and woods. One false step could be lethal, let alone the risk of creating a noisy cascade of stone.

‘It’s getting too dangerous,’ said Cooper. ‘Don’t you think so?’

‘I don’t know.’

Fry had begun to shiver. The damp and cold were insidious – they crept into your bones and clung to your clothes. No one in their right minds would be out here on a night like this, unless they had serious business.

‘What do you want to do, Diane?’

‘How far is it to the edge of the car park?’

‘Not more than a few yards now. It’s just past the slime ponds, where the route of the sough heads off towards the north.’

‘Oh, great.’

They moved on again, with Cooper paying as much attention to what might be going on around him as to where he was putting his feet. It was because of his lack of concentration that he was the one to stumble over a mine shaft and kick a scatter of small stones that rattled on the steel grille.

He looked up guiltily, expecting figures to appear from the fog. But the only shape he could see ahead was that of a lone, stunted tree, somehow struggling to survive between the spoil heaps. Its bare branches marked the outer perimeter of the mine.

Fry stood on a heap of stones and looked down at him.

‘Hurry up, Ben.’

They slid down the last few yards to the picnic area. But they were just in time to see tail lights disappearing back towards the road.

‘Damnation,’ said Fry.

‘I’m sorry,’ said Cooper. ‘That was my fault.’