Humankind rose from the carcass of a dead world. Lifetimes later, billions of people live in superstructures constructed atop the only habitable lands left, the Hawaiian Islands. Kilohana “Kilo” Ressler lives in Hawai'i City (known to the people as Big City) along with his illegal Digital Psychological Manifestation (DPM), EO, a pseudo-twin only perceptible to the host, designed during the rebuilding years to provide companionship in a world of horrors. Kilo has managed to keep EO a secret for most of his life, but when his skills are required for a diplomatic mission in Kaua'i City, Kilo and EO find themselves embroiled in a conspiracy that threatens to expose EO’s existence and endanger the fragile balance of power between the island cities. The only place left for answers is in the depths of the superstructure the Below. As the walls close in, Kilo must undertake the impossible task of protecting his friend, facing his past, and holding a crumbling city together.