The Wrong Sister
Starts as a simple tale of rich sister helping out poor sister with the use of holiday home in Venice with a few hints of a tradegy in the past. Very soon becomes much more complicated but in a convincing way, with new information gradually revealed and fairly believeable responses by the main characters. Moves to a satisfying conclusion that does explain everything and raises a moral dilemma that mirrors the events from the past.
Clever, well written and never dull. Certainly good enough for me to order another few books from this author.