Armed with secret knowledge, Juliette, now mayor of Silo 18 and her crew set out to rescue a world she hates but now understands better -- the world of the Silos with its rigid rules and terrible consequences for disobedience.

When Will Burrows and his friend Chester embark on a quest to find Will's archaeologist father, who has inexplicably disappeared, they are led to a labyrinthine world underneath London, full of sinister inhabitants with evil intentions toward "Topsoilers" like Will and his father.

As young archaeologist Will Burrows continues to search for his lost father in the strange underground world he has discovered beneath the city of London, he stumbles across a sinister plot with terrible implications for the world above.

In a ruined and toxic landscape, within a giant underground silo hundreds of stories deep, lives a society full of regulations they believe are meant to protect them. Then Sheriff Holston, who has unwaveringly upheld the silo's rules for years, breaks the greatest taboo of all: He asks to go outside. His decision unleashes a drastic series of events. His unlikely replacement - Juliette, a mechanic with no training in law, is about to learn how badly...