A young boy listens to his great-grandmother's tales of Green Knowe as it used to be and, gradually, as past and present blend, he shares the strange adventures of the former inhabitants.
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.
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.
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.