Das Gespenst der Gezeiten (The Witch of the Low-Tide)

Blurb

The Witch of the Low Tide, first published in 1961, is a detective story/historical novel by John Dickson Carr set in the England of 1907. This novel is a mystery of the type known as a locked room mystery as well as being a historical novel.
It is interesting from a modern viewpoint in that it deals with the sexual abuse of a child by her guardian where the sympathy of the writer is with the adult man and not with the underage girl.