The Bone Clocks by David Mitchell
Run away, one drowsy summer's afternoon, with Holly Sykes: wayward teenager, broken-hearted rebel and unwitting pawn in a titanic, hidden conflict.Over six decades, the consequences of a moment's impulse unfold, drawing an ordinary woman into a world far beyond her imagining. And as life in the near future turns perilous, the pledge she made to a stranger may become the key to her family's survival . . .