Margaret Peterson Haddix 
Under Their Skin [EPUB ebook] 

From New York Times bestselling author Margaret Peterson Haddix comes the first book in a crisp, intriguing, and thought-provoking (Booklist, starred review) new series about twins who are on a quest to discover the secrets being kept by their new family.Nick and Eryns mom is getting remarried, and the twelve-year-old twins are skeptical when she tells them their lives wont change much. Well, yes, they will have to move. And they will have a new stepfather, stepbrother, and stepsister. But Mom tells them not to worry. They wont ever have to meet their stepsiblings. This news puzzles Nick and Eryn, so the twins set out on a mission to find out who these kids areand why theyre being kept hidden.