Season 1

As the world's population is almost annihilated by a mysterious pandemic, accidentally unleashed by an unnamed Chinese scientist, the crisis is first seen through the eyes of two characters, Jenny Richards, a young working woman in London who is naturally immune to the disease, and Abby Grant, a middle-class corporate wife living a comfortable existence in a suburban commuter village who caught the virus but barely recovered, while her husband died. As Abby goes in search of her son Peter, who was away at boarding school when the pandemic occurred, Jenny wanders aimlessly through the countryside.

Other major characters introduced in the first few episodes are the resourceful engineer Greg Preston, the shifty Welshman Tom Price, and two children, John Millon and Lizzie Willoughby. Abby, Jenny, and Greg eventually come together and realise they must start again from scratch now that the civilization they once knew has been destroyed. After several adventures on the road, they find a property called The Grange which they can use as a base and, joined by other survivors, they form a potted community of disparate individuals all united by a shared purpose; to relearn the old skills of farming and tool-making, and to try to live in this new world.