Tolly comes to live with his great-grandmother at the ancient house of Green Knowe and becomes friends with three children who lived there in the seventeenth century.
The inhabitants of Green Knowe become involved with black magic when a modern-day witch attempts to find books of witchcraft supposedly hidden in the old house by a mad seventeenth-century alchemist.
A strange friendship develops between a young Chinese refugee who is spending the summer at Green Knowe and a gorilla who has escaped from the London Zoo.
An English girl, a Polish refugee, and a displaced boy from the Orient explore an island-strewn river flowing past the ancient manor house of Green Knowe.