‘My family are from West Yorkshire,’ said Irvine as they came in sight of the wind farm near Penistone.

‘I didn’t know that,’ said Cooper, who had assumed Irvine was of Scottish origin, what with his surname and the blue eyes, and the sandy hair.

‘Denby Dale, between Huddersfield and Barnsley. My Dad used to work in the mining-equipment industry, but his job went when all the pits closed down. So he got a job at Rolls-Royce in Derby. And the family moved down. I was only five at the time, so I don’t remember much about Denby Dale, except visiting my grandma.’

‘You never thought of going into engineering like your dad?’ asked Cooper.

‘No.’

Irvine said it so abruptly that Cooper wondered what the story was behind his decision to join the police. There was a long history of conflict between the police and men working in the coal industry, going back to the 1984–85 miners’ strike. Communities had been split, families divided, and the resulting bad blood had lingered for twenty-five years in some areas. He decided it might be better not to ask – until he knew Luke better, anyway.

‘I think we need to get on to the A636,’ said Irvine.

‘Sure.’

A few minutes later, Cooper steered the Toyota down a bumpy lane, following directions taken from a local. Sheltered behind a line of dense conifers, the slaughterhouse was almost invisible to a casual passer-by. Even if he’d been a rambler out on a stroll, he might not have seen it. The approach was via a long, winding lane that would have been difficult to find in itself without directions. At the end of the track was a collection of grubby stone buildings, devoid of any signs to indicate what they were. In the yard stood a row of steel-sided wagons that had brought animals for slaughter.

But once you reached it, and got out of the car, there was no mistaking what this place was. A distinctive smell filled the air. Blood, urine and dead flesh.

Cooper was no vegetarian. He liked a good steak as much as the next man. But the smell of meat in large quantities was cloying and sickly. It made him think of an old-fashioned butcher’s shop his mother used to take him to in town when he was a child. There had always been joints of meat hung all around the shop, and some had probably been there for days. It was one of those childhood impressions that could be brought back instantly by a smell like this.

The butcher’s was long gone now, of course. If his mother was still alive, she would be buying her meat shrink-wrapped from a chill cabinet at the supermarket, just like everyone else. That, or she would have found her own private source, which was still possible if you knew where to ask.

‘I hope we get masks,’ said Irvine. ‘I don’t think I can hold my breath until we get back to the car.’