Read a book once about a lady who stayed in a hotel on some deserted island (I think)? I think the book was written from her point of view but kept changing between her and the killer and it was a bit of a mystery as to which of the hotel guests was the killer? Spoiler alert I think it was a boy who was there with his mum or maybe it was the both of them.. sorry this is really vague. Sounds like a poirot plot but definitely wasn't that sort of book it was more modern... help