It seemed to Cooper that traces of pagan legacy were still there to be seen at every turn in this area, though few people noticed. They didn’t see them because their attention was focused on shop windows and traffic, the obsessions of modern society that overlaid history and pushed ancestral beliefs into the background. Now it was as if these ancient objects existed in an extra dimension, where they were only visible if you knew they were there and you looked straight at them.

There was a representation of Sheela-na-Gig incorporated into the stonework of St Helen’s Church at Darley Dale. The goddess of creation and destruction. Few people noticed it, surely, or understood its meaning. If they did, they’d be campaigning for its removal.

A couple of miles down the road, a display cabinet in Matlock church still contained a set of crantsies. Time-darkened maiden’s garlands, each one commemorating the death of an unmarried woman. Their wickerwork frames were decorated with symbols of purity – ribbons, roses, flowers of folded white paper – set around a centrepiece of a collar, a pair of gloves or a handkerchief, something that had belonged to the woman.

‘Is folklore important in Bulgaria, Georgi? I imagine it is.’

‘Yes, certainly. When I was very young, my grandmother gave me a book of Bulgarian fairy tales. The stories had many supernatural characters – werewolves, vampires, wood-nymphs. Lots of pictures. They stay in your mind when you’re a child.’

‘Yes, that’s right.’

‘I remember one fairy tale in particular. It told about a man who finds himself on another earth, in a different world. The only way he can get back to his own world is by riding on the backs of two eagles. But he has to feed the eagles with his own flesh so that they will carry him.’

Fairy tales weren’t really Cooper’s thing. But he knew some of them were supposed to have profound symbolic meanings, if you could manage to figure them out.

‘And what did that story teach you, Georgi?’

‘That sometimes it is necessary to sacrifice everything, in order to get to where you have to be. Even to sacrifice your own flesh and blood.’

‘I see.’

Then Kotsev smiled, his dark eyes glittering. ‘Also, that you should never trust eagles. Even when they say they’re doing you a favour.’

The Shogun had been abandoned under a bridge that was left over from a disused mineral line. It wasn’t even a bridge any more, because the central section had been removed. But it had only crossed a farm track anyway. By the looks of the deep tread on the wheel tracks in the mud, the farmer had probably passed the Shogun several times this week without bothering to report it.

A Traffic car stood guard on the road side of the bridge. But someone had done a good job of torching the Shogun. It was difficult to tell what colour the scorched paintwork had been, but for a few streaks left on the boot and around the front wings. The interior, though, looked relatively undamaged.

Cooper looked around the area. The last glance at the map had given him an idea.

‘There’s not much we can get from the car until the SOCOs arrive,’ he said. ‘I’d like to take a look up this way, Georgi.’

‘Very well. Your sergeant says you know everything about this area.’

‘She does?’

‘Yes, indeed. Sergeant Fry must regard you very highly.’

Cooper laughed. ‘I don’t think you’ve known her long enough. It probably wasn’t a compliment.’

Though Kotsev’s stride was longer, he obviously wasn’t used to walking over rough terrain, and definitely not uphill. He was panting in minutes. That was a sign of too much city living, in Cooper’s view. No matter how big their muscles were, a forty-five-degree slope always sorted the men from the boys.

‘Where are we going?’ gasped Kotsev, stopping to rest and watching Cooper moving steadily away from him.

‘Just to the top of this rise.’

‘Chaga, chaga. Wait.’

‘What’s the matter, Georgi?’

‘I think the air is a little thin here.’

‘We’re not even a thousand feet above sea level.’

Kotsev began to move again, but awkwardly, planting his feet with great deliberation on the rough grass. His knees were probably hurting by now, if he never used the right muscles.

A moment later, Cooper was standing at the top of the slope, letting the breeze cool his forehead. To the north east, he could see a drystone wall running along the skyline, marking the road between Wirksworth and Middleton. He followed the wall a little further north – and there was the distinctive outline of a red phone box.

He smiled. When public phone boxes were first designed, they were painted bright red to stand out from a distance. For decades, it had been important to know where the nearest phone was, and these old kiosks would have been a welcome sight. They weren’t used a lot nowadays. But they were such an integral part of the landscape that they were kept in the countryside as a conservation measure, as much as for emergency use.

Finally, Kotsev struggled the last few yards and arrived alongside him, breathing heavily and wiping sweat from his forehead.

‘Georgi, how many people in Bulgaria have mobile phones?’ asked Cooper.

Kotsev stared at him. ‘Everybody, except for those who are too poor. And the very old, who don’t understand them.’

‘Yes, it’s the same here. And even if you don’t own a mobile, you have a phone in your house. Not many people are too poor or too old for that.’

‘What are you saying?’

‘Well, it’s different, of course,’ said Cooper, ‘if you happen to live in a caravan.’

If he could have seen over the next hill, he might have been able to make out the red blob of a similar phone box in Bonsall Dale. That was the one Rose Shepherd had made two calls to. According to the map, it must be the nearest one to Lea Farm, where Simcho Nikolov had lived. Calls to the phone box by prior arrangement. Miss Shepherd had been in contact with Nikolov in the past three weeks.

Their connection supported speculation in the Bulgarian intelligence reports, a theory that Nikolov and Savova had been friends, or even lovers. Here was a link that had been more difficult to break than a mere business relationship.

Well, it was handy that rural phone boxes were marked on Ordnance Survey maps. But the box wasn’t what Cooper had noticed first. His eye had been drawn to the contour lines showing the steepness of the slope and the footpath above the bridge. It was funny the way things worked out sometimes.

He was turning to tell Kotsev that they might as well go back down to the burnt-out car, when two shots echoed across the hillside, one following quickly after the other. The flat smack of the first discharge sent birds scattering from the trees.

Kotsev looked around anxiously, and his hand went to his hip. ‘It’s stupid not to be armed. Why don’t they let you have guns?’

‘We don’t need them,’ said Cooper. ‘Most of the time.’

‘And the times when you do?’

‘We try to keep out of the way of the bullets.’

Kotsev snorted. ‘It’s stupid. You know this is the only police service in the world whose officers aren’t armed?’

‘No, there’s New Zealand too.’

‘New Zealand? But all they have to deal with are kangaroos. Here, you have armed gangsters, and terrorists. The IRA. Yardies. al-Qaeda. It’s stupid.’

Cooper laughed, and Kotsev glared at him.

‘Why are you laughing?’

‘I think you just don’t understand us, Georgi.’

There was a movement in the field ahead, and two figures appeared, walking rapidly down from the direction of the phone box. When they passed a stretch of fallen wall, the figures became identifiable as two men wearing peaked caps and quilted body warmers. Both of them had double-barrelled shotguns tucked under their arms.

‘So,’ said Kotsev. ‘Do we run away?’

As soon as Cooper walked back into the office at West Street, Fry slammed the phone down and glared at him. ‘See, I took my attention off Brian Mullen. I let him know he was under suspicion, and then allowed him the chance to do a runner. I should have been completing the case against him by now so we could make an arrest. But I was distracted. Too much attention on the Rose Shepherd enquiry. How can anyone be expected to do two jobs at once, and do them properly?’