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.

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.

The outer crust is under attack by the subterranean Styx who are turning ordinary humans into walking bombs and incubators for their eggs, and only Will Burrows and his band of retired commandos stand in their way--but the Styx also have problems of their own.

"Styx and their cohorts of deadly Armagi have swept across England, leaving death and devastation in their wake. Only a miracle can save the day and, in the inner world at the centre of the earth, Will and Elliott might just have stumbled upon one as they uncover ancient secrets that are fundamental to all human and Styx life"--

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...