He remembered that a few years ago the Duke and Duchess of Devonshire had cleared out their attics at Chatsworth House. They raised almost six and a half million pounds from the sale of valuable antiques and curiosities like the 6th Duke’s Russian sleigh and alabaster Borghese table. But no one would pay a fiver for this lot at Knowle Abbey. Even the seediest antique shop in Edendale would give it a pass. There were cases of crumbling butterflies and semi-precious stones, toy soldiers and porcelain dolls, stuffed antelope heads and sporting prints.

Cooper made a mental note to check on the earl’s gun licence. He felt sure there would be one. He imagined a cabinet full of shotguns somewhere in the house, perhaps even a few ancient blunderbusses and an elephant gun. Some poor licensing officer would have had the job of checking whether they were functional firearms or purely ornamental.

‘Yes, some of the Manby ancestors were avid collectors,’ said Meredith Burns. ‘The Victorians went in for natural history, and the eighteenth-century earls for religious texts. Of course, more than a few of them were army officers too.’

‘It’s amazing how much stuff they came back from Africa and India with,’ said Fry. ‘They must have used soldiers like packhorses to cart all their loot.’

There was a virtual tour of the state rooms on the first floor, an idea Cooper suspected had been copied from the National Trust, which had used them in its historic properties for years. He supposed it was an attempt to deter visitors from wandering around parts of the abbey where they shouldn’t go. But did it work? Well, it would take more than a glossy video and a bit of velvet rope across the doorway.

Cooper felt sure a determined and experienced snooper would have no trouble getting into any of the state rooms. There wasn’t exactly a high level of security. This was just someone’s home, after all. If an intruder could get into Buckingham Palace and chat to the Queen in her bedroom, there wasn’t much hope for an amateur set-up like this. The earl and his family would be sitting ducks, if someone had seriously decided to make them a target.

‘The private family apartments are in the west wing,’ said Burns. ‘Walter has an office of his own up there on the first floor, in the library. But many of the rooms in the north wing are now staff flats, offices, workshops and storerooms. Then we have these areas, which are accessible to the public. The visitor route alone is half a mile long. And it all gets vacuumed and dusted every day.’

They found themselves in the final doorway of a long corridor, gazing into apparent chaos. It was such a cluttered room. Every inch of floor space seemed to be crammed with furniture, and every available surface covered in ornaments and trinkets of no discernible use. How would you live in a room like this? He would hardly dare to move.

‘You can’t be serious about this threat?’ said Burns.

‘We do have good reason to be concerned. You should step up your security as much as possible, both in the abbey and around the park. We’ll have officers here to advise on additional security measures you can take. Also a dog unit will be arriving, in case there are already explosives on the premises.’

‘Our visitors aren’t going to like that,’ said Burns.

‘Visitors? Didn’t we say? We’re recommending that you close the abbey to the public for the time being, until we’re sure the threat has passed.’

‘That’s ludicrous. Have you any idea how much revenue we would lose? All our Christmas bookings would be cancelled, for a start. Walter would never agree to it.’

‘Could we speak to the earl himself perhaps and explain the situation?’

‘I don’t think so, Sergeant,’ said Burns stiffly. ‘Perhaps a more senior officer…’

Cooper nodded. He didn’t feel offended. Well, not as offended as Fry looked, anyway.

‘I’ll have a word with my superintendent,’ he said.

‘Yes, do that.’

Fry was staring with baffled revulsion at a huge glass cabinet full of stuffed birds. And it was full. There had been no half measures for this particularly fervent collector among the Manbys. Against a painted background of a seashore, he’d crammed in a heron, a couple of bitterns, a whole flock of curlews, turnstones and lapwings who crowded against each other in the foreground. A shelduck and a trio of plovers dangled from the top of the case in simulated flight. There was hardly an inch to spare between one set of feathers and the next.

And it was just one of many cases full of birds in this room. They were stacked right up to the ceiling on every wall. Some former earl must have been going for a complete collection of British bird species, thought Cooper, as he surveyed the room. Well, except for that pelican, resplendent in a case of its own, just about to swallow an equally stuffed fish.

‘What is your energy supply here?’ asked Cooper.

‘There’s a wood pellet-fuelled biomass heating system installed in a former agricultural building. It was one of Walter’s first projects when he inherited the estate. The system is fully automated and provides heating to various properties on the estate.’

‘Underground piping?’

‘Of course. About five hundred metres of it.’

‘Very vulnerable.’

‘Well, oil and electric storage heaters were the wrong sort of system to be using on such a big house, so investing in a green energy system seemed to be important. It lowers fuel costs and significantly reduces the estate’s carbon footprint. It even produces a financial payback through the government’s incentive scheme.’

‘One of his lordship’s most productive ideas, then.’

‘Precisely.’

They examined the main entrance with its wide steps and pillars, and a smaller side door where visitors paid their entrance fee. The locks were adequate, the alarm system modern. The earl would never have been able to get insurance for his historic mansion without those precautions.

‘I’ve been told the burial ground will be tarmacked over and become a car park for the holiday accommodation,’ said Cooper.

Burns shook her head. ‘That’s nonsense. We would never be allowed to do that, even if we wanted to. Most of it will remain an area of open space, with a bit of landscaping.’

‘I can’t emphasise enough how important it is to step up your security measures. There’s a good private security company based in Buxton. You should contact them.’

‘I’ll note your advice.’

Outside the main entrance, Cooper heard voices above him and looked up in astonishment.

‘Who are those people on the roof?’ he asked.

‘Oh, they’re a group of historic house enthusiasts,’ said Burns.

‘Members of the public?’

‘They paid twenty-five pounds each for a behind-the-scenes tour of the abbey today.’

The party had been led up a flight of narrow stairs from the top floor, through the attic, and out on to the roof, where they were able to gaze over the stone parapets at a mist-shrouded view of the Dove Valley. Directly below them was the crumbling Lady Chapel. They would have a good view of the missing tiles and the cracks in the walls. They would probably glimpse the corroded face of a stone angel. Or, if they were really lucky, they might witness an entire section shearing off the façade, like a calving glacier.

Cooper shook his head. Was there any point in wasting his breath urging extra security precautions when there was a crowd of complete strangers being allowed on to the roof?

They arranged to leave the park through the north entrance, taking a winding route through sheep pastures on the lower slopes of the hill, backed by more woodland. A member of outdoor staff was on hand to unlock the barrier and let them through.

Outside the north gate they were forced to slow to a crawl. A group of about twenty people were milling around with placards. Cooper stopped to speak to one of the two uniformed officers keeping a discreet eye on the demonstration.