I won't be the first to make this metaphor. I won't be the last. City of Ember meets the Goonies. 
 A fun quick read, especially if you don't think too hard about (view spoiler)[how much effort, contracting, costs, laborers, etc it takes to build a Secret City. It would have taken years to build, and hundreds if not thousands of employees. There is no way this installation would have been a secret. (hide spoiler)] 
 Especially after reading Sigler's Alive, it was such a relief to read a book about kids that had decent dialog and characters and didn't indulge in unnecessary violence. 
 Yes, it was tropey. Yes, it was unrealistic. Yes, it was fun. It's perfect for a movie. I liked it. 
 I still wish she'd write more about her Unicorns universe or at least more in that style of YA/Early Adult with tangible grit vs simple J.