Her Fearful Symmetry is sort of a mystery books. It features two sets of twins, American twenty-somethings Julia and Valentina and their English mother and aunt, Edie and Elspeth. At the opening Elspeth dies and leaves her apartment in London to the younger twins. Edie and Elspeth are estranged, haven't seen each other in decades, and Edie is forbidden from visiting Elspeth's apartment if the girls move in.
The girls are sort of a codependent dichotomy, Julia is strong, healthy and forceful and Valentina is ill and weak-spirited, but longs for independence. Elspeth the ghost is ever-present in the apartment and Niffenegger spends more time than you'd expect on the science side of the afterlife. She explains it from Elspeth's perspective as Elspeth discovers her ghostly nature.
As the story develops, there's an expected rift between the twins as Valentina falls in love with Elspeth's depressed boyfriend who lives in the apartment below and Julia befriends the obsessive compulsive that lives in the apartment above. Eventually, the story takes a bizarre supernatural twist and the truth behind the Edie/Elspeth rift is revealed.
I am not really a mystery-reader, so I'm not totally familiar with the usual plot devices, but I was pleasantly surprised by this book. There were some obvious red herrings and some leading foreshadowing, but the twist was still a surprise. While I had guessed the truth, I hadn't guessed the whole truth, nor did I see the ghostly hijinks coming. It was fun and I was amused by all of it.
As with The Time Traveler's Wife, Niffenegger gives the characters what they want and then makes them suffer for it a bit. The ending was far from happy, but when I finished I realized I wasn't sure who the protagonist was. The characters are each flawed, but their actions often belied their character so it was hard to root for anyone in particular.
I definitely recommend this book, it's a quick read but has a lot of interesting perspectives on death and truth and hurting the ones you love.
If they decide to make this into a craptacular movie like they did with Time Traveler, I'm hoping they cast the Olsen twins as Julia and Valentina. They are the right age and look and it would be an awesome way for them to reunite on screen. In what would definitely be a horrible movie.