‘Gavin, why don’t you find the offices and ask about CCTV footage? There’s a camera over the main entrance.’

‘All right.’

Cooper had seen signs on this floor for the working textile museum. Could it have been part of Miss Shepherd’s afternoon out, before her visit to the aquarium? Perhaps Arkwright’s legacy had some significance for her. Come to think of it, she was old enough to have worked here at the mill. Had she been revisiting old haunts, re-living memories one last time?

Cooper shook himself. He’d begun to imagine the victim having some kind of premonition that she was about to die. But no one knew the time of their death in advance, unless they had some terminal illness. Or they were intending to commit suicide. That was the only way to be really sure.

The museum was reached by leaving the shopping area and passing through an echoey room over uneven wooden floors that creaked and shifted underfoot, worn by decades of use by Arkwright’s millworkers. Bobbins and shuttles were on sale here, along with other mementoes of the textile industry that had once employed so many.

He found a man taking money on a flight of stairs that led down into the spinning and weaving sheds.

‘Do you issue admission tickets here?’ he asked.

‘No. You get a leaflet with a map of the route through the rooms of the museum – see?’

‘Were you working on Saturday?’

‘In the afternoon.’

‘Do you remember this woman coming in?’

The man looked at Cooper’s photograph.

‘No, sorry.’

In the rooms below, two enormous machines rattled away unattended, and stacks of shuttles sat in alcoves along the walls. There were wicker baskets and wooden trolleys, shelves full of old tools and equipment. An ancient typewriter, dusty cardboard boxes. Cooper could smell lubricating oil and hear the chug of the looms, leather belts spinning over wheels in the glass-roofed sheds. A tiny cubicle looked to be an overseer’s office, dusty ledgers still open on the desk, wire-framed glasses poking out of an ancient spectacle case. Visitors’ direction signs pointed towards a distant doorway – the bobbin room.

Cooper turned back. ‘Thanks for your time,’ he said.

In a distant corner of the shopping village, he found Eva Hooper. Her unit sold prints of Peak District landscapes, ethnic gifts, pottery, leather-work, gemstones. And, of course, a range of postcards, calendars and greeting cards – anything that tourists might be interested in.

‘Yes, I think she was here,’ she said. ‘It was Saturday, so we were quite busy.’

‘Yes, I understand.’

‘If it had been during the week, I might have remembered her better.’

‘Did she buy anything?’

‘I’m not sure. If she paid by cash, there won’t be any record of her name.’

‘OK.’

‘You could ask my assistant, but she’s not here today. She works for me part-time when I’m busy.’

‘What’s her name?’

‘Frances – we call her Fran.’

Cooper paused with his pen poised over his notebook. He’d spoken to a Frances very recently. It wasn’t a common name, but coincidences did happen …

‘Frances what?’

‘Birtland. She lives a couple of miles away, in Foxlow.’

‘Yes,’ said Cooper. ‘I know.’

Fry was satisfied that she’d done everything she could to prevent any further loss of evidence from the house at Darwin Street. She’d taken all the actions necessary to preserve the scene and create a log. The examination had been thorough. True, in an ideal world, it could have happened a bit sooner. But since when had this world been ideal? At least it had been done before any cleaning up or salvage operations started.

Now she was anxious to get Brian Mullen back at the scene as soon as she could, in case any more items came to light that needed to be recovered. Once that had been done, she could relax and let the clean-up get under way.

The good news from the fire officer was that significant evidence often remained, even after the most destructive of fires. She recognized some of the terms he used, but mostly his optimistic tone. The experts had even agreed on where the fire started, though apparently Quinton Downie had insisted on defining a radius of error about a metre around the likely source.

One of the SOCOs assigned to Darwin Street was Liz Petty. Some people turned up everywhere. Inside the hallway of the house, Petty was unpacking another holdall full of stepping plates.

‘Watch where you’re walking,’ she said, without looking round.

‘Yes, all right.’

She looked up then. ‘Oh. Hi, Diane. How are you doing?’

‘Fine.’

‘Making progress on the enquiry?’

‘Yes, thanks.’

‘There’ll be some publicity on this one, I suppose. There was a TV news van outside earlier. I don’t know what they were filming.’

‘They can film what they like. There’s nothing for them to see.’

She was aware of Petty watching her as she moved around the room. But after a moment, Fry became focused again. She was noticing all the changes that were taking place in the house – the plastic sheeting, the evidence containers, the yellow markers and flags that decorated the carpet, creating a bizarre new pattern on what had once been Lindsay Mullen’s cream Wilton.

‘Actually, I heard you weren’t getting on well with Quinton Downie,’ said Petty.

Fry turned. ‘Where did you hear that?’

‘People talk. Even firefighters have ears, you know. Otherwise, their helmets would fall off.’

‘Very funny.’

Petty looked up at her from her position crouched over a stepping plate. ‘Downie is very well respected in his field. He lectures regularly at Centrex.’

But Fry wasn’t impressed by the mention of the police training centre. ‘That doesn’t mean he has any right to lecture me.’

Downie was in the sitting room packing his equipment away. He looked satisfied with his efforts, reminding Fry of the fire service dog, the chocolate Labrador. He wasn’t quite wagging his tail, but it was a close-run thing.

‘Liquid accelerants are volatile, so it’s good that we collected debris samples early,’ he said when Fry entered. ‘Arsonists tend to use petrol products, because they’re easy to obtain and have a low flashpoint. But petrol has rather a narrow flammability range – it stops burning when the oxygen level is reduced. Hydrogen and acetylene are far more dangerous.’

‘The accelerant in this case could have been a butane-based lighter fluid.’

‘Butane? Well, the flashpoint is about the same as petrol, well below ambient temperature.’ Downie looked around the sitting room. ‘In fact, you’re lucky we’re not looking at radiation-induced flashover.’

‘What?’

‘In a closed room like this, there normally isn’t sufficient ventilation for unlimited burning. In fact, if it had been a bit more airtight, the fire might have gone out. But there was just a little bit of ventilation, and that made it worse. The room was pretty cluttered, items of furniture pushed close together, flammable materials on the floor. In conditions like this, flashover can happen very quickly. If you’re there to see it happen, it’s quite dramatic.’

‘OK, I believe you.’

Downie smiled, a man who enjoyed the small details of his job. ‘Old houses are the worst. A lot of them are like bonfires waiting for the first match. Wooden floors, wooden beams and window frames. With a bit of breeze blowing through, you can get a fire going that’s hot enough to melt the fillings in your teeth. Of course, it isn’t actually the wood that burns but the gases released from it by heat. The solid material disintegrates, and you’re left with a pile of ashes.’

‘But the victims died upstairs,’ said Fry. ‘Smoke inhalation.’

‘Oh, yes. Absolutely lethal. If you get a lungful of smoke from a house fire, you’re in trouble.’

‘I can’t understand why the victims never even made it to the stairs.’

‘Look, it goes like this …’ Downie demonstrated by closing his eyes and clutching his throat. ‘You’ve taken a breath and you can’t open your eyes because as soon as you do they water. You take another breath and the irritants hit the back of your throat. You retch and take an even deeper breath – it’s a natural, involuntary reaction. It fills your lungs with toxic fumes. That disorientates you, makes you dizzy, and puts you down on the floor. While you’re incapacitated, the toxicity takes over.’