Psychological thriller in the style of Nikki French or Sophie Hannah. Set in present day. Woman goes on a holiday to a house (maybe in Surrey) which turns out to be owned by her sister who has kept the fact hidden from the rest of her family. There is a locked study. Can't remember any of the more important bits of the plot (which is why I want to read it again!)
It's driving me nuts. Would be so grateful if this rings any bells for anyone.