I patted my way along the doorframe, feeling with my fingertips among the dust and little crunching lumps of dead insect, but there was nothing there.

It wasn’t on the floor either.

Could Jean have moved it? Or knocked it down while dusting?

Except, I had a crystal clear memory of putting the key up there after Jean left, just as Sandra had instructed, to keep it handy in case of an emergency but out of reach of the children. Could it have fallen down? But if so, what had happened to it? It was large and brass. Too big to go unnoticed on the floor, or to fit up a Hoover pipe. Had it got kicked under something?

I got down on my hands and knees and shone my phone’s torch under the washing machine and tumble dryer, but could see nothing under either, just flat white tiles and a few dust bunnies that quivered when I blew them aside. It wasn’t behind the mop bucket either. Then, in spite of my doubts, I went to the cupboard where the downstairs Hoover lived—but the dust chamber had been emptied. There was nothing in there. It was the bagless kind with a clear plastic cylinder that you could see the dust circulating in—even setting aside the question of whether the key could have got inside, there was no way anyone could have tipped out a big brass key without noticing it.

After that I scoured the kitchen, and even checked the bin—but there was nothing there.

At last I opened the utility room door and stared out into the rain towards the stable block, where a light had come on in the upstairs window. Should I call Jack? Would he have a spare key? But if he did, could I really bear for him to think me so disorganized and helpless that I had waited only ten minutes before taking up his offer of help?

As I was wavering, the light in his window went out, and I realized he had probably gone to bed.

It was too late. I wasn’t going to drag him out in his nightclothes.

After a last glance around at the yard directly outside the door, in case the key had got kicked outside somehow, I shut the door.

I’d ask Jack in the morning.

In the meantime, oh God, what would I do? I’d . . . I’d have to barricade the door with something. It was absurd—we were miles away from anywhere, behind locked gates, but I knew I wouldn’t sleep well if I felt the place was insecure.

The handle was a knob, not the kind you could put a chair under to stop it from turning, and there was no bolt, but at last, after a lot of searching, I found a wedge-shaped door stopper in the Hoover cupboard. I rammed it firmly into the gap beneath the door and then turned the doorknob to test it.

Somewhat to my surprise, it held. It wouldn’t stop a determined burglar—but then very little would. If someone was really set on breaking in they could just smash a window. But at the very least, it did give the impression that the door was locked, and I knew I would sleep more soundly because of it.

When I went back into the kitchen to clear away the pizza box and our plates, the clock above the stove read 11:36, and I could not suppress a groan. The girls would be up at six. I should have been in bed hours ago.

Well, it was too late to undo that. I’d just have to forgo a shower and get to sleep as quickly as possible. I was so tired, I was pretty sure that wouldn’t be a problem, anyway.

“Lights off,” I said aloud.

The room was instantly plunged into blackness, just the faint glow from the hallway illuminating the concrete floor. Smothering a yawn, I made my way up the stairs to bed, and was asleep almost before I had undressed.

When I woke, it was with a start, to complete darkness, and a sense of total disorientation. Where was I? What had woken me?

It took a minute for the memory to come back—Heatherbrae House. The Elincourts. The children. Jack.

My phone on the bedside table said it was 3:16 a.m., and I groaned and let it fall back to the wood with a clunk. No wonder it was still dark, it was the middle of the fucking night.

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.