It's summer, and Tuva is with Simen and his parents at their summer house on a small island in the south. At night, they are woken by a terrible noise, almost like a scream. On the way to the beach the next day, they hear snarling and rustling coming from the bushes. Their old neighbour thinks that the island is haunted. Tuva and Simen are not sure about that, but something scary is definitely going on. And when two nosy sleuths get wind of an unsolved mystery, no stone can be left unturned!