Twin powers

The description of those nieces, Julia and Valentina, might fit a pair of funerary statues: short, thin and pale, with white-blond hair and a tendency to hold each other's hands. They mirror each other even inside, where Valentina's heart sits on the right rather than the left and symmetry causes her a number of life-threatening health problems. Valentina is known as the nicer sister; perhaps inevitably, Robert finds himself falling for her, as she does for him. He is then in the awkward position of loving two women - one a living virgin, the other a phantom with an agenda. When Robert says of Elspeth's ghost, "her ideas have other ideas hiding inside them," it is an ominous observation, especially as Valentina enlists her help to break away from Julia.

Niffenegger's characters are selfish, messy, vulnerable and sometimes crazed, all under the attractive veneer of artistic and contemplative impulses. They don't live up to what others might consider their potential. Valentina wants to be a fashion designer but allows Julia's lack of ambition and general bossiness to keep her in a kind of perpetual adolescence. Martin is brilliant at languages, but his O.C.D.-­imposed confinement means he translates digitally submitted texts and constructs elaborate crossword puzzles destined to die along with the daily paper.

Even the most self-absorbed characters win a deep compassion; it's possible to root for every one, even as you want to shake some sense into them all. When he thinks of his wife, Martin misses her "roundness, he loved the warmth and heft and curve of her"; he even misses her snoring. Prickly Julia has her moments of kindness as she tries to help Martin. In part because of this emotional generosity, the novel is intimately and subtly humorous, as lovers banter and the narrative voice winks at human frailty. Put on a plummy British accent to pronounce "symmetry"and "cemetery" and discover a pun in the title.