Ardrossan is abuzz with rumours of ghostly sightings at the ruins of Ardrossan Castle. Some townsfolk claim to have seen the ghost of a long-lost noble wandering the grounds at night. Fear spreads, and the usually peaceful town becomes uneasy. Pat and his trusty dog, Stranger, along with their friends Joan, Bravo, Buff and Jamie, decide to investigate. As they dig deeper, they uncover a hidden passage in the castle and a secret that has been buried for centuries. However, someone else is determined to keep that secret hidden, and Pat's group must race against time to solve the mystery before it's too late.