Five Go to Billycock Hill is the sixteenth book in Enid Blyton's Famous Five series. The children rent a house near the remote Billycock Hill. The mystery involves a secret airbase or a research facility nearby, which is being spied upon by a dangerous gang. The Five stumble upon clues involving codes and signals. They must use their ingenuity to expose the spies and prevent them from stealing sensitive information, leading to a tense, modern adventure.
