‘The DSM doesn’t have a diagnosis for psychopathy,’ Dylan said. ‘But Keira – yes,Keira– told me that the closest thing is called something like “conduct disorder”.’ I could almost hear his brain whirring as he recalled what she’d told him. ‘Traits include a lack of remorse and feelings of guilt, callousness, a lack of empathy ...’

‘But they learn to mimic emotions, right?’ This was the kind of pop psychology I’d heard before. A staple of true crime documentaries and movies in which cops discussed the behaviour patterns of vicious serial killers.

‘Yeah, exactly.’

I shook my head. None of this was helping us find my wife and daughter, and it definitely wasn’t making me feel any better.

There was little else in the living room. A TV and a generous pile of magazines on a coffee table.Country LifeandTatler. Various others that focused on posh houses and luxury travel. I flicked through them and saw that they were well thumbed. Fiona hadtorn some pages out too, and made notes on others, circling items in lists of expensive furniture and fittings. Was this how she spent her evenings? Flicking through magazines dreaming of a five-star existence?

We went back into the hallway. Again, there were no pictures on the walls. No photos. Nothing personal at all, apart from a couple of coats hanging from hooks. It was like wandering through a show home, or a place someone had just moved into the day before. Dylan, who was texting Keira as he walked up the stairs behind me, didn’t seem to be impacted in the same way, but I found it deeply unsettling. Outside her home she seemed so normal. Friendly and full of opinions and interests. But if a person’s home reflects their personality, she was less than vanilla. She was blank.

Upstairs, we encountered more blankness. The landing also had plain walls. There were two rooms, the mirrored equivalent of Rose and Dylan’s rooms, that were completely empty apart from a few packing boxes that proved to have nothing in them. There had been part of me that had wondered if we might find possessions taken from Iris’s, but there was nothing here. No smoking gun that told me Fiona was a killer.

‘Not exactly a serial killer’s lair, is it?’ I said. ‘No photographs of victims pinned to the walls. No scrapbooks full of crazy scrawlings. No heads in the fridge.’

Dylan side-eyed me.

‘Sorry. It’s the tension. I can promise you I’m not actually finding any of this funny.’

‘I get it, Dad.’ He’d put his phone away. ‘I just want to know where Mum and Rose are, though.’

We were both silent for a minute, looking around the empty room we were in. There was a hollow, cold sensation in my stomach, and I kept thinking this must be a dream I was going to wakeup from. The kind that makes you laugh with relief when you re-enter the real world.I had the weirdest dream ...

‘Come on, let’s check the other rooms, and then I’m going to go and talk to the police.’

I poked my head into the bathroom, which actually looked used, with numerous bottles of shower gel and shampoo and creams. It was the only room that wasn’t spotlessly clean. The mirror was smeared, like someone had been writing on the glass with their fingertip, but I couldn’t make any sense of it.

Finally, we went into Fiona’s bedroom. I couldn’t help but feel guilty, invasive. If she was completely innocent, this was not cool of us. But the bedroom was as devoid of personality as the rest of the house. A double bed, plain white sheets; a bedside table with nothing on it except a lamp and a box of tissues. No books, no photos. I opened the drawer beside her bed, flushed with shame, aware that Dylan was watching me – a child, my son, being set this example. But the drawer had nothing in it except some mysterious tablets in a plain brown bottle, some lip salve, and some of the pages that had been ripped out of the magazines. I unfolded them, hoping they might tell me something useful, but they were just glossy photoshoots of expensive houses. The kind of places you see onGrand Designs, with glass walls and gleaming surfaces. An underground swimming pool and a garden full of bonsai.

There were no photos here. Nothing that would tell me who Fiona really was. I still didn’t even know for certain if Fiona Smith was a made-up name. This had been a wasted intrusion into her life and, although we hadn’t found anything embarrassing or private, I still felt dirty.

‘Let’s get out of—’

I froze. A phone was ringing.

‘That’s not your phone, is it?’ I asked, although I already knew the answer.

Dylan shook his head. ‘No.’

It was a noise that had once been omnipresent, but one I hadn’t heard in a long time: the old Nokia ringtone. It was faint, but the high-pitched beeps were still distinct. It kept ringing.

‘I think it’s coming from downstairs,’ Dylan said.

He was right. We both left Fiona’s bedroom – having refolded the magazine pages and put them back where I’d found them – and went back to the ground floor. I stood still for a moment, trying to figure out where the ringing was coming from.

‘The kitchen,’ I said.

We went in. The ringtone was muffled, indicating the phone was inside something or behind a door. I opened all the cupboards, including the ones I’d looked in earlier, and peered in. Same with the drawers.

Dylan looked up and said, ‘I think it’s coming from above our heads.’

There was a smoke alarm attached to the ceiling. I squinted up at it, confused. Was this smoke alarm ringing like a phone instead of emitting the usual shrill beeps that came out of them? I grabbed a chair, positioned it beneath the alarm and stood on it, reaching up to remove the cover.

Something dropped out. I tried to catch it but my reactions were too slow. Fortunately, Dylan had more time to see it and his reflexes were better. He caught it before it could hit the ground.

It was a tiny mobile phone that fitted in the palm of his hand. It did indeed look like an old Nokia, the kind everyone had once had, though I didn’t remember them being this small. And it was still ringing.

Dylan and I looked at each other, then I grabbed the phone and – carefully, because the buttons were so miniscule – answered it and put it to my ear.