Ruth Rendell’s final novel, Dark Corners, is about how psychological necessity can drive perfectly ordinary people either to terrible deeds or to unwitting acts of great courage — and extraordinary things can happen quite by chance to anyone.

Carl, the central character, is a young man pleased with his life. He has written a novel that has been published, inherited his father’s small mews house in Maida Vale with its furniture and, significantly, a large supply of alternative remedies in the bathroom cabinet, and has a beautiful, kindly girlfriend called Nicola.