We followed upstairs. I was relieved that the lights flickered back on as we did so, but when we opened the trapdoor it was only to find the tower full of birds. A few of them burst through the opening in a flurry of feathers and claws but, without the ability to dive from a height, they couldn’t build up any speed. When we peered up into the tower, we saw hundreds more there, their bright beady eyes staring down at us from the shadows.

It was a long and difficult climb. Fortunately the 300gannets seemed to take fright at being in such a small space, and many of them flapped off out of the broken windows to be swallowed up by the storm. Those that remained watched us silently from the bannisters, their eyes shining in the dark.

Sheets of rain lashed in, making the stairs slippery, and my heart sped up in my chest as we neared the top. It wasn’t only the ghost I dreaded – my fear of heights was making me feel panicky too. I knew the tower probably wasn’t going to come crashing down, but it was hard not to think that it could, especially with the wind and rain howling so savagely around it.

We looked into the Strangers’ Room, but it was empty, so we returned to the staircase and continued to climb. I licked salt from my lips as we reached the lantern room at the very top and cringed at the thought of how high up we were. I knew if I hesitated now then I might flee the lighthouse and never look back, so I forced myself forward and stepped over the threshold.

The huge windows up here were stormproof, and most of them were intact, apart from one that was partly smashed right at the top. There were bits of 301broken glass and dead gannets scattered everywhere. Several live birds flew around the tall room too. The revolving light made their shadows into gigantic, winged monsters for a moment before shrinking them back down to small specks.

I thought at first that we were alone in the lantern room, but then I spotted a small figure standing at one of the windows – a child dressed in rags. Even facing away from me, I saw that he was horribly thin. And there were dreadful wounds on his arms and legs, raw and red and messy. It took me a moment to realize what they were, but then I remembered my own injured leg and shivered. Those were eel bites.

I felt a great, powerful rush of sympathy that took the edge off my fear as I walked over and stopped behind him. Now that I was closer, I could hear that Conall was muttering a name under his breath. “Charlie! Charlie! Charlie!”

I took a deep breath and crouched down to his level.