Cooper shuddered. Everyone thought they might be losing it at some time in their lives, didn’t they? It didn’t necessarily indicate a deeper problem.

But occasionally, such ideas did rise from the depths of his mind to settle on the surface, like a scum of decomposing leaves. It was best not to disturb them. They were black and slimy with putrescence. Leave them alone, and they’d sink to the bottom again, vanish in a bubble of gas. That was the best way. He wished Matt would understand it.

11

Flowers had started to arrive at Darwin Street. Floral tributes to Lindsay Mullen and the two children. They came from relatives, friends and neighbours, and even from people who’d never known them. Communal grief had become fashionable, even in Edendale.

Next door, Keith Wade was complaining to a uniformed constable that he’d had to park his car at the end of the road because of the outer cordon. Fry saw that he was still wearing the same sweater. It must smell like a badger by now. No wonder Mr Wade lived alone.

And, of course, the fire investigator from the Forensic Science Service had arrived at Darwin Street when Fry wasn’t looking. As a result, he’d already assessed the scene and was setting out his equipment in the Mullens’ sitting room when she found him.

‘Glad you could make it,’ she said. ‘DS Fry.’

He was a small, middle-aged man whose white paper suit emphasized his pear-shaped body. And when he spoke, he revealed a Scottish accent.

‘Quinton Downie,’ he said, taking off a glove to shake hands.

‘Do you have all the background information you need?’

‘All that you can give me, apparently.’

‘You know the time of the call to the fire service, and the apparent seat of the blaze, based on the firefighters’ observations. We can’t tell you anything about the contents of this room.’

‘Yes, yes. So what is my objective? The cause of the fire? Mode of spread? Want me to comment on the accuracy of witness statements?’

‘The cause of the fire will do for now, thank you.’

‘Just so we’re clear. It would be very useful to examine photographs of the scene during the fire.’

‘Oh?’

Downie looked up at her. ‘Try asking around the neighbours – someone may have taken photos or videos of the fire. It’s amazing how often the offender stays on to watch the fun.’

‘It’s already been done. Right now, I just need you to concentrate on your own job.’

‘OK. So … Locate seat of fire. Consider possible ignition sources. Excavate seat?’ Downie tilted his head to one side and looked at the charred remains around him. ‘Yes, I think so. Then take samples, formulate hypotheses. And report conclusion.’

‘I’ll look forward to it,’ said Fry.

Downie was unpacking what looked like a series of pre-prepared forms. ‘You’ll get a location plan, as well as photographs as I excavate the seat of the fire. Samples will go straight to the lab.’

‘Fine.’

‘By the way, I examined the outside of the building before I came in. Do you know that you have unsooted broken glass in the vicinity of a side window?’

Fry had been about to leave the room, but turned back. ‘What?’

‘A broken side window. I wondered if your people had noticed it already. There don’t seem to be any markers round there.’

‘A lot of these windows are broken,’ said Fry. ‘That’s the result of heat from the fire, surely?’

Downie looked up and smiled. ‘If that were the case, the glass would be sooted on the interior surface. It isn’t, which implies it must have been broken either in the early stages of the fire – or before it started.’

‘You mean a point of entry?’

‘Could be. I took samples anyway. But you might want to get that window examined for fingerprints or tool marks before the evidence is compromised any further.’

‘You don’t have to tell me my job.’

Downie just sniffed, as if she wasn’t even worth a reply.

Fry glared at the back of his head as he continued to lay out his equipment. Looking around for someone to give instructions to, she caught sight of the fire officer standing in the doorway, grinning.

At that moment, her phone rang. It was the sergeant in charge of the search team.

‘I thought you’d want to know straightaway, we’ve found an empty lighter fluid can. It’s butane, but quite an unusual brand, I believe. It looks like someone found a use for a hundred millilitres of Swan Extra Refined recently.’

‘Where did you find it? How near the house?’

‘It had been chucked in a wheelie bin a hundred yards down the street, near the corner of Lilac Avenue. The householder says no one at this address smokes, and she has no idea how the can got in her bin. She insists it wasn’t there on Sunday when she last put some rubbish out.’

‘You’ve got it bagged properly?’

‘You bet.’

‘Thanks.’

Fry ended the call and turned back to Downie. ‘Show me this side window,’ she said.

He sighed and stood up. Together, they made their way out of the house and into a side passage near the garage. Brian Mullen’s car still stood on the drive. It was a red Citroën, almost the same colour as the fire appliances that had surrounded it on Sunday night.

‘OK,’ sighed Downie. ‘Look, you have plumes of soot deposited on the exterior wall by smoke emitted from the window. But the broken glass on the ground beneath the window is unsooted. So, we can conclude that the fire didn’t touch this glass.’

‘Yes, I see.’

‘Even from here, I can see tool marks on the window frame,’ said Downie. ‘You might care to check whether the firefighters obtained entry this way.’

‘They didn’t. They came in through the doors.’

‘Right.’ Downie turned to look at her. ‘Pity about the shoe impressions, though.’

‘What shoe impressions?’

‘Precisely.’

Fry looked at the ground where they were standing. It was a muddy mess, covered in crushed vegetation and trampled by size ten boots.

‘Shit.’

Downie shrugged. ‘Think yourself lucky to get this much. The site of any fire is a challenge to the principles of crime-scene management.’

‘If the lab finds butane in your samples, it won’t be up to me any longer anyway, lucky or otherwise,’ said Fry. ‘It becomes a murder enquiry.’

‘I know, I know.’

Fry felt herself getting angry. ‘Three people died in this fire. The evidence mustn’t be compromised.’

‘I can assure you, Sergeant Fry, everything will be done by the book.’

Fry looked at the rest of the houses in the street. A few neighbours were clustered outside the cordon. By the book, eh? That was all she needed, some civilian lecturing her about procedure. She knew what ‘by the book’ meant.

She also knew the principles Downie was referring to: protect, record and recover. Crime-scene examiners said that contamination only really occurred after the scene had been preserved. Anything before that was normal procedure.

But in this case, procedures had involved smashing down the doors and flooding the place with water, then sending in firefighters in big boots to trample the sodden evidence. Well, the principles still applied. As long as compromises were recorded and reasons given.

‘By the way,’ called Downie, passing the RV point on the way to his vehicle, ‘the usual advice is not to fit a smoke alarm in the kitchen. Steam and cooking fumes can set it off too easily. For a two-storey house like this, the bottom of the staircase is the best location, with a second one on the landing as an extra precaution.’

‘I’ll be sure to let Mr Mullen know,’ said Fry.

‘Who?’

‘The householder. The husband of the dead woman, the father of the two dead children. He’s in hospital right now, but I’m sure he’ll be pleased to know that he installed the smoke alarm in the wrong place. I bet it’s the information he’s been waiting to hear.’