Death and the Maiden — Gladys Mitchell

When former banana-grower Edris Tidson hears of the possible sighting of a water-naiad he insists that his wife, her aunt Prissie and Prissie's young ward Connie, travel with him to Winchester in search of the nymph. As tensions rise between Connie and Edris, Prissie invites the renowned psychoanalyst, and unrivalled detective, Mrs Bradley to join them and unofficially observe Edris and his growing obsession. Then two young boys are found drowned and speculation mounts that the naiad is luring them to her deaths. Can Mrs Bradley unravel the mysteries hidden within the river?