Then a tiny flash of colour caught her attention. A glint of bright yellow, like a drop of sunlight in the blackness. She crouched towards the floor and gently blew away the ash. A broken section of Monopoly board lay at her feet: Piccadilly and the Water Works.

Of course, the untreated polyurethane foam in the furniture had been the real problem. Brian Mullen had definitely had a point. Lindsay could have spent her money more wisely if she’d replaced the cheap sofa instead of the carpet. The outcome really could have been different. For a start, her children might still be alive.

When she walked through into the kitchen, Fry found it almost pristine and untouched, apart from a few muddy footprints on the vinyl flooring. From the condition of the teak-effect units and the white painted walls, she would never have guessed there had been a fire at all. She felt as though she’d stepped out of one film set and into another, where an entirely different story was taking place. This one suggested a harmless domestic comedy – a family eating breakfast together in their spotless kitchen, Mum and Dad and the kids, all chattering and laughing, hurrying to get ready for work or school. Behind her, the other room might have been the scene of a cheap horror film, except the credits had already rolled and the crew had packed up and gone home.

‘Diane, do you want to have a look upstairs?’ called Murfin, without enthusiasm.

‘Yes, in a minute.’

Fry took a last look at the kitchen, with its silent smoke alarm. She noticed that the cooker was new, too. A Smeg dual-fuel with air-cooling system. A thousand pounds or so, she guessed. Money wasn’t all that short in the Mullen household, after all.

She went back through the sitting room and joined Gavin at the foot of the stairs. She wasn’t sure that she needed to visit the bedrooms. They might have been where the victims died, but they weren’t where the fire had started. If there had been a crime committed, it was here on the ground floor that the evidence would be found, surely?

As she was debating with herself, Murfin settled the question by hauling himself slowly up the stairs, sighing at every step. Fry had no choice but to follow him.

And, in a way, the bedrooms weren’t quite so bad. It was clear that the flames hadn’t reached here. The furniture was almost untouched, though covered by a layer of soot. The covers of the beds had been pulled back, revealing clean, unmarked sheets. The first room she saw might simply have been waiting for Lindsay Mullen to come home and clean up the mess. Apart from the markers where her body had lain when she collapsed from smoke inhalation, of course.

‘Have you got the photos there, Gavin?’