They’d carried on past the entrance to Magpie Mine, leaving the lights of Elder’s Nissan turning into the picnic site. They knew where he was, and he surely hadn’t come all this way for no reason.

Cooper had turned off the engine of the Toyota and wound the window down to listen. There was no other traffic on the road, not within half a mile or so. Whether there was a vehicle already parked at the picnic site, they couldn’t tell without getting too close.

‘Are we going to have to call it off, Diane?’ he said.

‘No chance.’

‘We can’t drive any nearer. They’d hear us coming.’

‘Reverse into the mine entrance, and we’ll walk from there. Have you got a torch?’

Cooper produced two maglites from the glove compartment, and they got out of the car. He’d driven his car on to the verge, turning swathes of dead leaves to mush under his tyres. Fry slithered her way through them on to the gravel, and they began to walk back into the remains of the mine.

Of course, the gateway and the first few yards beyond it were a quagmire. Someone had chosen to avoid the rutted track and drive across the soft, uneven ground, churning even more ruts in the process. Cooper heard Fry cursing under her breath as she slipped and squelched, trying hard to make as little noise as she could.

Somewhere in the darkness, cattle were sleeping. Cooper could hear them breathing, so loud that they could have been right next to him. Fog had that peculiar effect – it muffled distant sounds, so that noises closer to hand seemed to be amplified.

‘Are you sure we should be doing this, Diane?’ he said.

‘Ben, for the past week people have been trying to push me to the sidelines of this enquiry. I’m not going to prove anyone right in their opinion of me by giving up now. I’m not going to give them the chance of saying that DS Fry packed up and went home because the weather was bad.’

Cooper couldn’t see her face properly, but he could hear the tension in her voice and he knew she was serious. This was important to her.

‘I understand,’ he said.

‘Good.’ Fry’s breath puffed out in clouds, mingling with the fog. ‘Now – are you with me, Ben? Or not?’

‘Of course I’m with you.’

As they picked their way carefully on to the site, the banging of corrugated-iron sheets met them again.

‘God, I wish someone would fix those loose sheets,’ whispered Fry, disturbed by the noise.

‘I think Elder’s car will be this way,’ said Cooper as they passed the front of the agent’s house. ‘Watch your step. There’s an underground flue that runs between the old winding engine and the chimney, and its roof has collapsed in places. Don’t fall into it.’