Vomit suddenly rises in my throat and fills my mouth, and I turn my head, spewing it onto the ground. I feel weak and dizzy from the concussion. I can’t move my left arm. My thoughts are disjointed and confused, floating past me like soap bubbles on the breeze. Every time I try to catch one it bursts in my hand.

I must pass out again, because I’m jolted back to consciousness by a sudden burst of bright white light: the harsh glare of an overhead bulb. It takes several minutes for my eyes to adjust, but finally my mind is coming back into focus. I remember what happened: looking for Peter and Stacey, finding Felix, the sudden blow to the back of my head. I have no idea how much time has passed: a few minutes, an hour, a day.

I glance at Felix on the metal bed next to me. He’s not moving. I can’t see the rise and fall of his chest. I don’t know if he’s still alive.

I try to move towards him, and my left arm screams in protest: I’m handcuffed to the same metal pipe as Felix. One tug tells me it’s not coming free.

‘Ah. You’re back with us,’ Stacey says.

She’s standing in the doorway to the small root cellar, safely well out of my reach. I try to speak, but only manage a harsh cough. She points to a bottle of water next to me. Pain shoots through my tethered arm from my wrist to my shoulder as I jam the plastic bottle against my chest so I can open it with my free hand. The water is tepid, but it clears my throat.

‘Where’s Peter?’ I rasp.

‘He’s here,’ she says vaguely. ‘Sorry about the headache,’ she adds. ‘I’m afraid this was the only way.’

‘Where is he?’

‘I told you, he’s here,’ she says impatiently. ‘You’ll see him soon enough.’

Adrenaline is an extraordinary hormone. It’s an amazing thing to have coursing through your system when facing danger – people have been known to lift a car off a child with its help. It increases the flow of blood to muscles, releasing sugar into your bloodstream, along with a cascade of other effects that make your body alert and more able to fight off an attacker or outrun a flood.

My mind is suddenly crystal clear. Stacey deliberately left the door to the cellar open. She knew I was coming to the house to collect Peter: she wanted me to find it.

She wanted me down here, in a cellar no one knows exists.