Book excerpt: Get ready for another heart-racing, twist-filled thriller from the #1 NEW YORK TIMES bestselling author NATASHA PRESTON. CAN YOU TRUST YOUR OWN TWIN? After their parents divorced, 10-year-old twins Ivy and Iris were split up - Ivy lived with Dad, Iris with Mum. But after a tragic accident takes their mum's life, the devastated sisters are reunited when Iris moves in with Ivy and their dad. Iris takes their mum's death especially hard, unwilling to speak to anyone except Ivy. Unable to stand seeing Iris so sad, Ivy promised her that she can share her life now. After all, they're sisters. Twins. It's a promise that Iris takes seriously. And before long, Ivy's friends, her teachers, and even her boyfriend all fall under Iris's spell. Slowly, Ivy feels she's being pushed out of her own life, but tells herself she's being paranoid. Iris isn't dangerous . . . is she?