Margaret Peterson Haddix 
In Over Their Heads [EPUB ebook] 

Nick and Eryn must figure out a way to save the world without sacrificing their newly discovered family in this follow-up to Under Their Skin, which Booklist called ’;crisp, intriguing, and thought-provoking’ in a starred review.In Under Their Skin, twins Nick and Eryn successfully met their new stepsiblings, Ava and Jackson. But in doing so, the twins found themselves on a mission to discover how to prevent humanity from facing certain doom. Now, their two families are joined together to save not only themselves, but everyonehuman and robotic. Can they figure out how before it’s too late?