She considered Brian Mullen again. He was one of only two people she could definitely place at the scene around the time of the fire. Mullen had a key to the house, so he wouldn’t have needed to break in through the side window. Of course, the damage to the window might simply have been a blind, to make everyone think there had been a break-in.

She wondered whether she ought to have seized Mullen’s clothes for forensic examination at an early stage in the enquiry. But it would have been a pointless exercise, even immediately after the incident. Mullen had legitimate reasons for his clothes being impregnated with smoke, or even singed by the fire. He’d tried to get into the house to rescue his children, hadn’t he? He had plenty of witnesses to that fact, including the two firefighters who’d physically dragged him back to the pavement. It took a bit of clever forward planning to contaminate forensic evidence like that. She couldn’t believe Brian Mullen had it in him.

But no, she shouldn’t rule out it out completely. No more false assumptions.

Gradually, Fry found her thoughts focusing on Keith Wade. The perfect neighbour, the assiduous member of Neighbourhood Watch. The keen amateur photographer. The only other person she knew to have been at the scene when the fire started.

Fry paused and checked her email. Wade had promised to send her some of his photos, but they hadn’t arrived yet. She doubted if they ever would.

Then another thought struck her. Brian Mullen had an alibi for the time of the fire – he’d been at the Broken Wheel with Jed Skinner until the early hours of the morning. In Wade’s case, it was that very same fact that had made it possible for him to get into the Mullens’ house. If Brian hadn’t been out late that night, the front door of number 32 would have been bolted on the inside. But Lindsay had left the bolts off for her husband to come home. Wade could have known that quite easily, couldn’t he?

There was one person who wasn’t out with the search teams. He wasn’t on duty because he was at home, recovering from his unexpected dip in the trapped waters of the Derwent. Fry dialled his number.

‘Ben,’ she said, ‘can I bounce something off you?’

‘Yes, I’m fine. Thanks for asking, Diane.’

‘Oh. Well, I can tell you’re all right by the way you sound.’

Cooper sighed. ‘What did you want to bounce off me?’

‘Brian Mullen. You know that he denied the arguments with his wife?’

‘Yes.’

‘Whose word do we have that those arguments ever took place?’

Cooper considered the question for a moment. ‘Well, the lady on one side of the Mullens heard the row about the carpet.’

‘Which is the only one Brian admits to. And the rest?’