Uncle Quentin wants some peace so The Famous Five are sent to stay with Mrs Leyman. Her grandson Wilfred reluctantly joins them in exploring a mysterious island which is said to be haunted. The children spot two men carrying heavy boxes through the woods. When they return to their boat, It has gone! They will have to stay on the spooky island until Mrs Leyman realises they are missing, Dick discovers a small door In a well-shaft which leads into a cave full of old art treasures. Wilfred wanders along the cliffs and spots the two men emerging from a cave below carrying paintings. Just as he and the others find their way into the cave, Carlos and Emilio return. After a desperate struggle the children are locked In the cave - the same cave that Dick discovered earlier) As they escape through the secret door to the well-shaft Emilio and Carlos return. Timmy comes to the rescue and both men are locked in the cave as the Five flee. The children are still trapped on the island, but they are safe from the villains - or so they think. Suddenly Carlos and Emilio charge out of the woods. For a moment the situation is dangerous but Uncle Quentin arrives on a police boat in the nick of time. Mrs Leyman has raised the alarm and the villains who have stolen precious works of art from all over the country, are caught red-handed.