But the pain didn’t come – only another boom as the second barrel was discharged. And then a high-pitched scream that split the air, amplified by the fog into an awful ear-bursting noise.

The smell of burnt gunpowder filled Cooper’s nostrils, hot and acrid. This wasn’t potassium nitrate cooking in the kitchen at Pity Wood Farm. This was the real thing, and far more deadly.

Cooper found himself spread flat on the ground, his face pressed to the concrete, trying desperately to dig himself into the floor, the taste of stone in his mouth. He became aware that Fry was close beside him, her body pushed up against his, seeking any inch of safety.

They waited, afraid to move or breathe, until they heard footsteps heading away over the spoil heap, back towards the cars. Cooper felt Fry begin to tense, as if she was going to stand up. He grabbed her arm and pulled her back down.

‘Wait!’

Her face was close to his now, and he could see her eyes glinting with fear and excitement.

‘Someone is being killed,’ she said. ‘We should do something to stop it.’

‘Like what? We’re not armed. Remember the first rule is to protect your own life, otherwise you’re no use for protecting members of the public.’

‘I’m the senior officer here, Ben.’

‘So? Are you going to get us both killed to prove something? That won’t impress Superintendent Branagh, you know.’

‘Bastard,’ she hissed. But she stayed down, waiting until they finally heard a car engine start up. A vehicle passed slowly along the roadway towards the agent’s house.

‘OK?’ she said.

‘OK. But take it slow and quiet.’

When they emerged from the door, nothing was moving outside. Two bodies lay in the mud, still wearing their balaclavas. A double-barrelled shotgun had been broken open and left on the roof of Cooper’s Toyota. There was no sign of David Palfreyman.

Fry and Cooper stood looking at the bodies, knowing that they shouldn’t touch anything, wondering how they’d managed to survive. They looked up when more headlights swung across the mine buildings and lit up the engine house. They were ready to run again. But they saw the blue flash, and they knew it was finally their back-up.

After that, they were surrounded by a familiar chaos. More and more vehicles arrived with their lights flashing – paramedics, armed response, the duty inspector, the whole circus.

To Fry and Cooper, trying to recover from the adrenalin still surging through their bodies, it all seemed to be going on around them in a dream. DI Hitchens appeared, and Cooper thought he saw Superintendent Branagh in the fog, but she didn’t speak to either of them.