Deep beneath Monstrocity lies the Great Machine, a powerful super-computer that controls the heat vents that give the city its power. It is enormous and ancient, and some, like Preacher Mandoras, believe it to be alive. It holds the key to humankind's salvation.

After the vile Dream Factory is closed down all its prisoners are set free – onto the inhospitable streets of Down Below. Gardener Bee must somehow find a way to survive.

Meanwhile, Tyler, Tourmaline and Kinsey recruit the intelligent but eccentric Down Below cybernetician Dr Henry Hartwell to continue their education.

Starving, unable to find work, Bee is inspired by a rousing sermon from Preacher Mandoras to join him.

Unfortunately for Tyler, Tourmaline and Kinsey, Dr Hartwell is unstable with a chequered past. Bee discovers the Great Machine is not the benevolent being it appears to be. The enlightenment it offers comes with a terrible price.