I pushed down my irritation and made myself smile pleasantly.

“Hello, girls, were you playing hide-and-seek?”

“Yes,” Ellie said with a giggle, but then she remembered our earlier quarrel, and frowned. “You hurt my wrist.”

She held it out, and there, to my chagrin, was a ring of bruises on the pale skin of her stick-thin wrist.

I felt my cheeks color.

I thought about arguing with her, but I didn’t want to raise the issue in front of Mrs. McKenzie, and besides, it seemed like I’d done enough to antagonize them both today. Better to swallow my pride.

“I’m ever so sorry, Ellie.” I bent down beside her at the breakfast bar so that our heads were on a level, speaking softly so that Mrs. McKenzie wouldn’t hear. “I truly didn’t mean to. I was just worried you’d hurt yourself on the drive, but I really apologize if I was holding your arm too hard. It was an accident, I promise, and I feel terrible about it. Can we be friends?”

For a second, I thought I saw Ellie wavering, then she jerked and gave a little whimper.

Beneath the breakfast bar I saw Maddie’s hand whip back into her lap.

“Maddie,” I said quietly, “what just happened?”

“Nothing,” Maddie said, almost inaudibly, speaking to her plate more than me.

“Ellie?”

“N-nothing,” Ellie said, but she was rubbing her arm, and there were tears in her bright blue eyes.

“I don’t believe you. Let me see your arm.”

“Nothing!” Ellie said, more fiercely. She pulled down her cardigan and gave me a look of angry betrayal. “I said nothing, go away!”

“Okay.”

I stood up. Whatever chance I had had there with Ellie, I’d blown it for the moment. Or rather Maddie had.

Mrs. McKenzie was standing against the counter, her arms crossed, watching us. Then she folded the tea towel and hung it over the stove rail.

“Well, I’ll be away now, girls,” she said. Her voice, when she spoke to the children, was softer and far more friendly than the terse, clipped tone she’d used with me. She bent and dropped a kiss on top of each head, first Ellie’s blond curls, then Maddie’s wispy dark locks. “You give your wee sister a kiss from me, now, mind.”

“Yes, Mrs. M,” Ellie said obediently. Maddie said nothing, but she squeezed Mrs. McKenzie’s waist with one arm, and I thought I saw a wistful look in her eye as her gaze followed the woman to the door.

“Goodbye now, girls,” Mrs. McKenzie said, and then she was gone. Outside I heard a car start up and bump down the drive to the road.

Alone in the kitchen with the two little girls I felt suddenly drained, and I sank down on the armchair in the corner of the room, wanting nothing more than to put my face in my hands and bawl. What had I taken on with these two hostile little creatures? And yet, I couldn’t blame them. I could only imagine how I would have reacted if I’d been left for a week with a total stranger.

The last thing I could cope with was losing the children in the grounds again, so while they finished up their cookies, I crossed into the hallway and examined the inside of the big front door. There was no key—no keyhole even, as I’d observed the very first time I had arrived. Instead, the white panel I had noticed contained a thumb sensor—Sandra had programmed my thumbprint into her phone app earlier that morning, before she left, and shown me how to operate it.

There was a matching panel on the inside, and I gingerly touched it, watching as a series of illuminated icons sprang into life. One of them was a big key, and remembering Sandra’s instructions, I tapped it cautiously, and heard a grinding click as the deadlocks inside the door slid home. There was something rather dramatic, even ominous about the sound, almost like a prison-cell lock grinding into place. But at least the door was secure now. There was no way Maddie or Ellie could even reach the panel without a set of steps, let alone activate the lock, since I very much doubted Sandra would have programmed their fingerprints into the system.

Then I went into the utility room. The door there operated with just a regular lock and key—as if Sandra and Bill’s budget had run out, or as if they didn’t care about the servants’ entrance. Or maybe there was some practical reason one door needed to be traditionally operated. Something to do with power cuts or building regulations, perhaps. Either way, it was a relief to be faced with technology an average person could figure out, and it was with a feeling of satisfaction that I twisted the key firmly in the lock and then tucked it away on the doorframe above, just as the binder had instructed. We keep all keys for the doors operated by traditional locks on the doorframe above the corresponding door, so that they are handy in case of emergency but out of reach of the children, the paragraph had read. There was something comforting about seeing it up there, far away from little fingers.

Mission accomplished, I went back into the kitchen, my best and brightest smile firmly plastered on.

“Right, girls, what do you say we go through to the TV room and watch a movie. Frozen? Moana?”

“Yay, Frozen!” Ellie said, but Maddie butted in.

“We hate Frozen.”

“Really?” I made my voice skeptical. “Really? Because do you know, I love Frozen. In fact I know a sing-along version of Frozen where they have the words on the screen and I’m really good at joining in on all the songs.”

Behind Maddie I could see Ellie looking desperate but too scared to contradict her sister.

“We hate Frozen,” Maddie repeated stubbornly. “Come on, Ellie, let’s go play in our room.”

I watched as she slid down from her stool and stomped into the hallway, the dogs’ eyes following her with puzzlement as she went. In the doorway she paused and jerked her head meaningfully at her sister. Ellie’s bottom lip quivered.

“We can still watch it if you want, Ellie,” I said, keeping my voice as light as I could. “We could watch it together, just you and me. I could make popcorn.”

For a minute I thought I saw Ellie hesitate. But then something in her face seemed to harden, and she shook her head, slid from her stool, and turned to follow her sister.

As the sound of their footsteps faded away up the stairs, I sighed and then turned to put on the kettle, to make myself a pot of tea. At least I would have half an hour to myself, to try to figure out the situation.

But before I had even finished filling the kettle, the baby monitor in my pocket gave a crackle and then broke into a fretful coughing cry, telling me that Petra had woken up, and I was back on duty.

No rest for the wicked then.

What had I taken on?

I know I’m going on. And I know you must be wondering when the hell I’m going to get to the point—to the reason I’m here, in this prison cell, and the reason I shouldn’t be.

And I promise you, it’s coming. But I can’t—I can’t seem to explain the situation quickly. That was the problem with Mr. Gates. He never let me explain properly—to show how it all built up, all the little things, all the sleepless nights and the loneliness and the isolation, and the craziness of the house and the cameras and everything else. To explain properly, I have to tell you how it happened. Day by day. Night by night. Piece by piece.

Only that sounds as if I’m building something—a house perhaps. Or a picture in a jigsaw. Piece by piece. And the truth is, it was the other way around. Piece by piece, I was being torn apart.