Stupid brain.

But what the hell had woken me? Was it Petra? Had one of the girls cried out in their sleep?

I lay for a moment, listening. I could hear nothing, but I was a floor away, and there were two closed doors between me and the children.

At last, suppressing a sigh, I got up, wrapped my dressing gown around myself, and went out onto the landing.

The house was quiet. But something felt . . . wrong, though I couldn’t put my finger on it. The rain had stopped, and I could hear nothing at all, not even the far-off roar of a car, or the whisper of wind in the trees.

When the realization came, it was in the shape of two things. The first was the shadow on the wall in front of me, the shadow cast by the wilting peonies on the table downstairs.

Someone had turned the hall lights on downstairs. Lights that I was sure I had not left on when I went to bed.

The second came as I began to tiptoe down the stairs, and it made my heart almost stop and then begin beating hard enough to leap out of my chest.

It was the sound of footsteps on a wooden floor, slow and deliberate, exactly like the other night.

Creak. Creak. Creak.

My chest felt like it was constricted by an iron band. I froze, two steps down, looking at the light on the landing below, and then up at where the noise seemed to be coming from. Jesus Christ. Was someone in the house?

The light I could have understood. Perhaps Maddie or Ellie had got up to use the loo and left it on—there were dim little night-lights plugged into the wall at intervals, but they would probably have switched on the main hallway light anyway.

But the footsteps . . . ?

I thought of Sandra’s voice, suddenly coming without warning over the sound system in the kitchen. Could that be the answer? The bloody Happy app? But how? More important, why? It didn’t make sense. The only people with access to the app were Sandra and Bill, and they had no possible motivation to scare me like this. Quite the reverse, in fact. They had just gone to enormous trouble and expense to recruit me.

Besides, it just didn’t sound like it was coming from the speakers. There was no sense of a disembodied noise, the way there had been with Sandra’s voice in the kitchen. There, I’d had no impression of someone standing behind me, talking to me. It had sounded exactly like what it was—someone being broadcast through speakers. This, though, was different. I could hear the footsteps start on one side of the ceiling and move slowly and implacably to the other. Then they paused, and reversed. It sounded . . . well . . . as if there was someone pacing in the room above my head. But that made no sense either. Because there was no room up there. There was not so much as a loft hatch.

An image suddenly flashed into my head—something I hadn’t thought of since the day I arrived. The locked door in my room. Where did it lead to? Was there an attic? It seemed improbable that someone could have entered through my room, but I could hear the footsteps from above.

Shivering, I tiptoed back into my own room and flicked the switch on the lamp by my bed. It didn’t turn on.

I swore, Mr. Wrexham. I’m not too proud to admit it. I swore, long and loud. I had turned that light off by the switch, so why the fuck wouldn’t it turn back on by the switch? What kind of sense did this stupid lighting system make anyway?

Furiously, not caring about the music or the heating system or anything else, I mashed my hand against the featureless panel on the wall, bashing randomly at the squares and dials as they illuminated beneath my palm. Lights flickered on and off in closets, the bathroom fan came on, a brief burst of classical music filled the air and then fell silent as I jabbed at the panel again, and some unseen vent in the ceiling suddenly began to blow out cold air. But finally, the main overhead light came on.

I let my hand fall to my side, breathing heavily but triumphant. Then I set about trying to open the locked door.

First I tried the key to my bedroom door, which Sandra had shown me, tucked away on the doorframe above the door, like the others. It didn’t fit.

Then, I tried the key to the wardrobe on the other side. It didn’t fit either.

There was nothing above the doorframe except a little dust.

Finally, I resorted to kneeling down and peering through the keyhole, my heart like a drum in my breast, beating so hard I thought I might be sick.

I could see nothing at all—just unending blackness. But I could feel something. A cool breeze that made me blink and draw back from the keyhole, my eye watering.

It was not just a cupboard inside that space. Something else was there. An attic, perhaps. At the very least, a space big enough to have a draft and a source of air.

The footsteps had stopped, but I knew that I would not sleep again tonight, and at last I wrapped my duvet around myself and sat, my phone in my hand, the overhead light blazing down on me, watching the locked door.

I don’t know what I was expecting. To see the handle turn? For someone—something—to emerge?

Whatever it was, it didn’t happen. I just sat there, as the sky outside my window began to lighten and a thin lemon-yellow streak of dawn crept across the carpet, mixing with the artificial light from above.

I felt nauseous with a mix of fear and tiredness, and dread of the day ahead.

At last, when I heard a low fractious wail come from downstairs, I loosened my grip on my phone, flexed my stiff fingers, and saw that the display said 5:57 a.m.

It was morning. The children were waking up.

As I crawled from my bed, my hand went up involuntarily to touch my necklace—but my fingers grazed only my collarbone, and I remembered that I had taken it off that first night, spooling it on the bedside table, just as I had done before the interview.