After London is set in an England reclaimed by nature at some unspecified point in the future. Due to the baleful influence of a mysterious Unknown Orb, which came within Earth's orbit centuries earlier causing a catastrophic effect on tides, the planet's magnetism, nature and the minds of men, civilisation is overthrown – floods devastate the cities and very little remains of former times, akin to post-Roman Britain in the Dark Ages.
Knowledge of advanced technology has been lost and a feudal medieval state exists, with castles, barons, sieges, etc. The majority of the country is dominated by a vast woodland and by lakes which cover much of the landmass. Domesticated animals have escaped and turned feral; others have died out. The wildwood is inhabited by bandits, bushmen and gypsies. Much of Britain is ruled by 'hostile' tribes – Welsh, Scottish, Irish, reclaiming former kingdoms. The few settlements are protected enclosures, based on the medieval estate. Central Southern England (primarily, the Vale of the White Horse) is covered by an enormous lake. London is a toxic wasteland.
A post-apocalyptic London is at the dark heart of the book. It is echoed in the history of the Twentieth Century and in popular culture. It shares a similarly nightmarish aesthetic to Cormac McCarthy's Pulitzer-prize winning novel The Road – an uber-bleak novel depicting a burnt America, the result, as in Jefferies' novel, of an unspecified catastrophe, which has resulted in 'the fragility of everything revealed at last'.
Jefferies' London is also echoed in Ridley Scott's haunting vision of a dystopian future, Blade Runner (1982) – based upon Philip K Dick's Do Androids Dream of Electric Sheep? – particularly in the opening sequence.