The River at Green Knowe: The Green Knowe Chronicles, Book Three

L.M. Boston's thrilling and chilling tales of Green Knowe, a haunted manor deep in an overgrown garden in the English countryside, have been entertaining readers for half a century.

In this, the third book, Tolly and his grandmother are away (presumably in Cornwall). Two women have rented the house for the summer and ask three children to stay. Ida is the niece of one of the women; Ping and Oskar are refugees. The children are turned loose on the river, where they have many fine and imaginative adventures.