Sister is two sisters: the one gone and the one left behind. Those two sisters, Beatrice and Tess, are intensely close but physically separated by an ocean. While Bee has been advancing her career in NYC, Tess is attending a London art school. One day Bee gets a call. Tess has gone missing. Then Bee gets The Call. Tess has been found dead in a public restroom. The police have reason to rule the death a suicide. Tess had been through an unhappy love affair and in quick succession a pregnancy shadowed by a diagnosis of cystic fibrosis and the death of her infant son. Easy-peasy for the police to decide her death was a suicide.
Bee doesn't believe that her sister would have killed herself and dedicates herself to finding Tess' murderer. She goes to London against the advice of her Mother and fiancee and immerses herself in Tess's old life. Beatrice soon discovers that murder is not the only mystery Tess left behind. Bee finds a few very likely suspects: Tess' married teacher lover, a drug addicted fellow student, a well respected doctor and a top man in a bio-med company.
Those are the bones of this stylish and clever mystery/thriller by Rosamund Lupton. The how-well-do-you-really-know-someone and the no-one-knows-that-this-was-really-murder plot elements are as old as Wilkie Collins but Lupton has remade them with insight into multidimensional relationships and some nice, spooky originality. She has written Sister in the form of a long, confessional letter from Beatrice to Tess. This technique underscores the level of intimacy between the sisters and immediately makes the reader a part of that relationship and therefore have an added stake in the search for answers. Sister is a persuasively suspenseful and satisfying novel.