Jack, Rosie, and their cousin Finn expect a quiet summer in a remote coastal town, until they uncover a mysterious old map pointing to an island that doesn’t appear on any modern chart. With Ava, a fearless local sailor, they set out to investigate. What begins as a simple adventure quickly becomes something far more dangerous. Strange markings, abandoned structures, and a hidden threat beneath the island’s surface turn their holiday into a race for answers. A thrilling tale of courage, friendship, and the secrets that lie beyond the edge of the known world.