The Castle of Adventure (published in 1946) is a popular children’s book by Enid Blyton. It is the second book in The Adventure Series. The first edition of the book was illustrated by Stuart Tresilian.
Jack, Lucy-Ann, Dinah and Philip attempt to figure out what is behind the strange goings-on at a ruined castle near Spring Cottage in Scotland where they are on holiday with Dinah and Philip’s mother, Aunt Allie. The four youngsters make friends with Tassie, a mysterious gypsy living in the woods with her mother.
Along with Bill Cunningham, who appears later in the book, the children manage to expose a ring of spies led by the threatening Scar-Neck who are working against the UK Military service.