The Pact by Jodie Picoult

AZ: "For eighteen years the Hartes and the Golds have lived next door to each other, sharing everything from Chinese food to chicken pox to carpool duty. Parents and children alike are best friends - so it's no surprise that in high school Chris and Emily's friendship blossoms into something more. They've been soul mates since they were born. When the midnight calls come in from the hospital, no one is prepared for the appalling truth: Emily is dead at seventeen from a gunshot wound to the head as part of an apparent suicide pact. The gun holds a single unspent bullet that Chris tells police he intended for himself, but a local detective has doubts. And the Hartes and Golds, in a single terrifying moment, must face every parent's worst fear: do we ever really know our children at all?"

Picoult is now an author I turn to with relief, becuase as with Francis, Koontz, Faulkner and Jasper Fforde, I know that what I'm about to read will be a pleasure. The Pact is the desperately sad story of two children who grow up next door to each other (Em and Chris) and as teenager begin going out together. Em is conflicted in two ways, one by loving Chris very deeply but there being incestuous elements of brotherly love, and by a moment of sexual assault that drives her to self-loathing and suicidal tendencies.