The Mountain of Adventure (Piper)

Mrs Mannering thinks that a peaceful holiday in the Welsh mountains couldn't possibly land the children in another dangerous adventure. How wrong she is! Philip, Dinah, Lucy-Ann and Jack are soon up to their necks in the mystery of a rumbling mountain, roaming wolves, and a mad genius who plans to rule the world. Other titles in the "Adventure" series include: "The Island of Adventure", "The Castle of Adventure", "The Valley of Adventure", "The Sea of Adventure", "The Ship of Adventure", "The Circus of Adventure", and, "The River of Adventure".