The Famous Five: George, Julian, Dick, Anne, and their dog Timmy, are spending their first holidays together and right away they plunge into an exciting adventure. On a day out at the beach, they make a chilling discovery in an old smuggler’s cove and realize that George’s father Quentin, a famous inventor, is in grave danger! The professor has set up a lab on a rocky island, where he’s researching a new method of generating energy. But it seems someone else is interested in his findings. Unfortunately, neither the police officers Peters and Hansen nor George’s mother Fanny believe the children, so the Famous Five set off in pursuit of the dangerous gangsters themselves. The clues lead them to two suspicious wildlife photographers and a mysterious man claiming to be an agent. Finally, the Famous Five discover a secret passage under the sea that takes them to the rocky island, where they uncover a conspiracy they can’t barely believe.