Julian, Dick, Anne, George and Timmy the dog are thrilled when Uncle Quentin announces he will conduct a secret scientific experiment on Kirrin Island. But George senses something strange—her father is behaving oddly, and mysterious figures have been seen watching the island. When Uncle Quentin becomes secretive and even the children discover they are being spied upon, the Five begin to investigate. Soon they uncover a gang of dangerous men plotting to steal Uncle Quentin's valuable scientific secrets. Timmy disappears, George takes matters into her own hands, and once again the Famous Five find themselves in the middle of another thrilling adventure.
