There is a ruined castle on Finniston Farm, but only the dungeons remain and no one knows where they are! The Famous Five are determined to find them, and whatever else is hidden inside, but someone else wants to find out too. Can the Five get there first?
We commence this adventure in Blyton's beloved Dorsetshire. The opening chapter's title is almost a book title in itself—"Five are all Together Again". Julian and Dick are holidaying on their own to start with. It is not clear as to why, but Julian says, "Good thing Anne didn't come—she'd have given up the first day." "George wouldn't have minded," Dick replies. "She's game for anything." As Ju says, it is fun to be on their own, but things start to happen when the four of them are together (Five you mean, Dick points out!).