New York Times bestselling author Margaret Peterson Haddix, the master of cliffhangers, delivers a pulse-pounding mystery perfect for fans of Jacqueline West and Kat Yeh, full of secrets, surprises, and the power of family. One minute they're there: laughing and having fun at the house next door. The next minute, the teens are gone. Like magic. Marin can't believe her eyes. Who are they? Can anyone else see them? What makes...