Starred Review Twelve-year-old twins Nick and Eryn aren't terribly surprised when their mother informs them she is getting remarried; she and Michael have been dating for several years. Moving to a new house won't be so bad, since they will go to the same school, and they will still alternate weeks at their father's house like always. But when she tells them that to ease the transition they won't be meeting their new stepsiblings, Ava and Jackson, Nick and Eryn's curiosity is piqued, and they can't stop devising plans to get in touch with the new kids. When they finally figure out where Ava and Jackson live, they see something that shocks them to their core. The book's underlying secret is well thought-out, supplying explanations while still building tension. The major question readers will want answered is the one Nick and Eryn want answered, too, and when it's revealed at the end of this first of a two-book series, it raises the already high tension level through the roof. Haddix, author of the Missing series, does a particularly fine job of catching the nuances of both kids and the adults, each with their own agendas. A crisp, intriguing, and thought-provoking tale that's hits the bull's-eye for its middle-grade audience.