Her Fearful Symmetry by Audrey Niffenegger
When Elspeth Noblin dies she leaves her beautiful flat overlooking Highgate Cemetery to her twin nieces, Julia and Valentina Poole, on the condition that their mother is never allowed to cross the threshold. But until the solicitor's letter falls through the door of their suburban American home, either Julia nor Valentina knew their aunt existed. The twins hope that in London their own, separate, lives can finally begin but they have no idea that they've been summoned into a tangle of fraying lives, from the obsessive-compulsive crossword setter who lives above them to their aunt's mysterious and elusive lover who lives below them and works in the cemetery itself. As the twins unravel the secrets of their aunt, who doesn't seem quite ready to leave her flat, even after death, Niffenegger weaves together a delicious and deadly ghost story about love, loss and identity.