James and Jessica are staying with their friend Maddie at Daleton Farm. On their first day, James finds an old bottle in the nearby lake, with a message inside. It starts with the word HELP. The writer is a young boy who signs himself Michael, and he's begging to be rescued from the small island in the middle of the lake, where he says he's a prisoner. The note is forty years old, and they think it must be part of a game that was being played by the village children. But they quickly discover that the note is part of a very dark story. When Maddie flies her photographic drone over Daleton Lake, they see something mysterious under the water. Why are the owners of Daleton Hall trying to keep them away from the lake with scary stories, and why do they angrily deny ever having had a son called Michael?