My voice echoes and bounces against the walls, and I glance up at the windows high above us, and then back to him. His face is taut with anxiety and I think he might leave, but he shakes his head.

‘No, come on.’

He says it without a smile and I start climbing again before either of us can change our minds. The wind howls and pummels the stone walls, and the suck and slap of the waves is so loud it sounds as if the sea is crashing into the lighthouse itself.

I run up another flight of steps, then make the mistake of leaning over the railing and looking down. The ground speeds away and I stumble back, my head spinning with vertigo.

‘Are you OK?’

Tom appears on the stairwell beneath me. He’s moving as quickly as he can, but I can tell his ankle is hurting him. I start to answer when another low rumble sounds overhead. We hold one another’s gaze and Tom’s eyes fill with warning. The noise fades, until there’s only the sound of the wind whistling through cracks in the stone.

My mum’s voice calls out from above and I grip my locket. I don’t understand the words – they sound like another language, Latin maybe, but I can tell she’s afraid. I start to run again, and am almost at the top when Tom shouts.

‘Ivy, wait!’

I turn around and he winces in pain.

‘I can’t keep up. My ankle.’

My mother yells something, her voice panicked.

‘Please, Tom, go back to the house.’

He says something, but I don’t stop to listen. I race up the last few steps and pass through a wooden door, surprised to enter an empty room with an iron ladder fixed against one wall. From the vivid light flooding down, I’m guessing I’m in a service area that leads to the lantern.

Grabbing the rails of the ladder, I climb up and see a white domed ceiling with curved walls made from dozens of panes of glass. The circular space is surprisingly small, most of it taken up by a two-foot-high metal platform that holds the lens in the centre. Tall and thin, it looks like half a dozen balls of glass placed on top of one another.

Squinting at the brightness, I step off the ladder and onto the metal walkway that surrounds the lens. My mother stands to my right, her back pressed to the wall. She wears a long black robe, her face a ghoulish red. She glares at me and then jerks her head to the side.