From New York Times and USA Today bestselling author Jamie Thornton.

A surprise mutiny.

Dessa and her friends reach the safety of the surface, mourning the death of one of their own, only to discover everything has changed. Old alliances have failed and more than half of Sanctuary's staff mutiny?they will do whatever it takes to wrest control of Sanctuary from the scientists.

Sanctuary is fighting a civil war, but the kids from Project Polus are trapped deep underground with Super V's on the loose and on the hunt.

Dessa and her friends must risk it all to raid Sanctuary, save the kids, and make their home safe again. But what if Sanctuary can't be saved?