The stairwell is unlit. Using the torch on my phone, I grope my way carefully down the dangerously steep flight of concrete steps, one hand on the rough stone wall for balance. When I reach the bottom, I find the cellar floor is beaten earth, the ceiling so low I have to dip my head to avoid hitting it on the old beams. It must be an ancient root cellar. I can’t imagine it’s been used in years.

‘Peter?’ I call again. ‘Stacey?’

I cast my torch around me. The cellar is about ten feet square, and there’s nothing in it but a few broken tools. Everything is covered with a thick layer of dust and cobwebs. It looks like no one’s been here in decades.

I almost miss it at first, concealed as it is by a partial collapse of the ceiling, but then I see it: another door directly opposite the stairs. Two heavy bolts at top and bottom have been pulled back from their locks. Drag marks scored in the earthen floor show it’s been opened, and very recently.

My heart pounds as I grab the doorknob and pull. It’s black as pitch in here: without the daylight spilling down the stairs from the house above, this room is even darker than the root cellar. My field of vision is restricted to the narrow circle illuminated by my phone torch. But I can feel cold air on my face: there must be a vent or duct to the outside somewhere.

I yelp as my shin makes contact with cold metal, and swing my phone down.

‘Oh, dear Christ,’ I whisper.

Felix is still alive, stretched out on a bare, stained mattress atop a narrow metal bed frame. He shrinks back from the sudden glare of light, turning his head away with a gargled yelp.

I drop to the floor beside him. ‘It’s going to be OK,’ I tell him. ‘I’m here now. I’m going to look after you. I’ll get you out of here.’

The bottom half of his face is oddly black, and it takes me a moment to realise it’s not dirt but dried blood. The stench coming off him tells me he’s been lying here in his own filth for weeks: I can smell not just urine and excrement, but the sickly-sweet decay of sores and infected wounds.

His pulse is weak and thready, but it’s there. He tries to speak, but the most he can manage is a thick, choking sound. His eyes bulge frantically. I hook my finger in his mouth, trying to clear his airway. When I remove it, several of his teeth spill into my hand.

‘Dear God,’ I mutter, appalled.