Seven detached houses comprise Heron Close, a rural settlement by the side of an East Anglian estuary. Susan Swann is a young teacher sharing a house with its owner Miss Kant, a retired lecturer. Also on the Close are the elderly Whitwhams, middle-aged Patrick Dawson, and the widow Eva Maitland. They are a fairly typical bunch, thinks Susan, but then something happens to disturb the calm of the little Close on the evening of a summer party. And worse is to follow.