Back in the hallway, I stopped, my gaze falling on the photographs under the stairs, the pictures hanging like fruit. There was no device here, no place to disguise it, but it was clear that the technology in the living room and kitchen would have been powerful enough to register conversations at a distance. It would have recorded the exchange I’d had with Ross the day before as we’d stood in front of the picture tree. I didn’t remember us saying anything revelatory – but that hardly seemed the point.

Someone had been listening.

Someone wanted to know what I was saying.

A creak on the landing. I came around the stairs and looked up. Healy was standing at the top, waving me towards him. He’d found something. I was pretty sure I knew what it would be, and when I got to Patrick Perry’s office I saw that I was right: another device, attached with duct tape to one of the legs on Patrick’s desk, hidden from view.

I pointed to the device, then to the floor, and held up a couple of fingers, indicating I’d found two more downstairs.

Healy mouthed, What the hell?

I put a finger to my lips and cupped my ear.

They can hear everything.

Inside ten minutes, we’d found two more.

One was in Patrick and Francesca’s bedroom, hidden in a false panel at the top of one of their fitted wardrobes; a second was in an air vent in the bathroom, placed there – I was guessing – because the bathroom represented the midway point of the first floor and would therefore be able to pick up sounds from all directions.

I led us downstairs, put on my shoes and headed out of the house, out of the gate that marked the start of Black Gale and beyond that for forty feet.

‘What the hell’s going on?’ Healy said, once we’d stopped walking.

‘You really need me to answer that?’

‘You think that Mills guy put those things in there?’

‘I don’t know,’ I said, ‘but he seems like a pretty good place to start.’

I looked at the Perrys’ house and then at the others. Were there bugs inside all four properties? We’d need to make sure, but – given the way Isaac Mills had checked the sides of the other homes in the same way as the Perrys’ – I was willing to bet there were. It explained something else too that I’d been trying to figure out: how Mills had seemed to know who I was, even before asking. It was because those same bugs had recorded my visit to Black Gale the day before and he’d heard Ross using my name.

‘How did the police miss these?’ Healy asked.

‘Because there was no crime here.’

He looked at me, instantly understanding.