SISTER by Rosamund Lupton

This literary mystery has more murder suspects than a game of Clue.  Still, the police insist that Tess's death was a suicide.  In the meantime, her sister Beatrice puts herself in harm's way, as she becomes obsessed with identifying Tess's killer.  Beatrice loses credibility with the police when she finds that too many of Tess's male acquaintances had a motive for doing her in.  First, there's her married lover and tutor, who tried to squelch the scandal of Tess's pregnancy.  Then there's the son of a prominent politician who had a huge, unhealthy crush on Tess and stalked her with his camera.  Finally, there's the shady medical trial of an in utero gene therapy that was supposed to cure Tess's unborn child of cystic fibrosis, but the baby was stillborn, due to an unrelated issue.  A need to expunge her own guilt, as well as a thirst for justice, drives Beatrice's quest.  Beatrice finds that she has not been the model sister and daughter that she thought herself to be, and now it is too late to make amends with Tess.  Tess, however, was a free spirit who, if she were alive, would tell Beatrice that there is nothing to forgive.  Tess gave completely of herself, while expecting nothing in return.  This book succeeds on a literary level because of its treatment of the bond between the two sisters that persists even after one has died.  However, I don't have a sister, and for me, the twists and turns and wide array of villains, one of whom must be the murderer, were what kept me reading.