I used the cairn to warn Mia that there was a fourth, unexpected stranger on the island. I hadn’t been able to believe it at first – the chances of it seemed so impossible – and it wasn’t until Liam and I found the squatter’s campsite in the castle that I put it together and realised we weren’t alone.

I wanted to pull the plug immediately on our plans and left another note for Mia in the cairn, but she wouldn’t have it. We’d come this far, and she thought it worth risking it. She believed whoever was holed up in the castle would leave us alone, not wanting to get caught. And they did leave us alone. The problem was that Liam thought that they were the person who had stood at the window watching us; that they were responsible for the etching of the word ‘DEVIL’ on the window and the electricity being cut and the food being stolen and the woodpile being wrecked, when in fact it was Mia who had done it all. When I lay in bed listening to her scratching the word ‘DEVIL’ into the window downstairs, I was terrified that Liam would wake up and catch her. I couldn’t sleep for fear he was on to us.

I tried everything I could to keep Liam away from the castle, to stop him from confronting the stranger, but of course he wouldn’t listen.

When he discovered the boathouse, I had no time to warn Mia, and so the only thing I could do was to throw myself out of the boat. I knew if we left the island then that was it – all our plans would have been for nothing. So, even though Liam has left me terrified of water, as soon as he took his eyes off me to look over his shoulder, I launched myself over the edge of the boat and into the freezing waters of the loch. If I drowned, I told myself at least I would die on my own terms and it would be my choice.

I was the one, too, who left the glass angel on the ground by Liam as he slept. Mia wanted him to see it; she believed it would be the final puzzle piece that would jolt his memory and make him realise who was stalking him and why. But when I woke up, I remembered the story Mia told me of how she’d fled through the snow with her feet bleeding, glass splinters embedded in them, and so I placed it where I knew Liam would step on it.

I wanted to make him suffer; to let him have one more taste of his own medicine.