I stared down at the paper. Surely Charlie hadn’t written this? The writing seemed too grown-up and neat for him. And I noticed now that the piece of paper was thick and crinkly and yellow, like it was old. I guessed Charlie must have found the letter somewhere and used the back of it for his drawing. 136My mind went to the logbooks and documents upstairs in the tower. I was just wondering whether Charlie could have found his way up there when the trapdoor suddenly shifted to one side and down climbed Charlie himself. He started guiltily when he saw me and darted into his bedroom, but I followed him and closed the door behind us.

“Charlie, you shouldn’t have been up there,” I said. “What were you thinking?”

“We were only playing,” he replied, sticking out his lower lip.

“We?” I repeated. “Who’s ‘we’?”

“Me and my friend. We were exploring the tower.”

I guessed he must have some kind of imaginary friend, which was confirmed the next moment when Charlie said, “No one else can see him.”

“Well, both of you keep out of the tower from now on. You heard what your mum said about the lightning strikes. It’s not safe.”

“OK,” Charlie said cheerfully enough. “It’s boring up there anyway.”

He scampered off and I stood for a moment, worrying about what to do. Maybe I should tell Dad and we could find some way of locking the door 137again. But when I suggested as much to Rosie later that day, she was crestfallen and begged me not to.

“I’m getting the most fantastic photos!” she exclaimed. “And if I carry on then I just know I’ll capture something supernatural on film before we leave. I can feel it!”

Even though I knew it was a bad idea, I gave in to Rosie, just like I always did. So I agreed to leave the trapdoor open and keep it a secret from Dad and Kate.

It wasn’t until much later that I’d realize this was the biggest mistake of my life.

That night Rosie was still extremely keen on the idea of sleeping in the Strangers’ Room, but the storm was raging worse than ever so I told her it was absolutely not an option. In the end she reluctantly agreed to set up her digital camera on video-recording mode in the room and collect it the next morning.

We lay down to sleep in utter darkness as usual. I would never have admitted it to Rosie, but I found the complete lack of light a bit unnerving. At home, I was used to street lamps shining through the 138curtains, and it still seemed unnatural for it to be so pitch-black, with nothing to help my eyes adjust to the dark at all. I almost envied Charlie his night light.