It is seven years after the first outbreak of "the Sweats" destroyed the world, almost overnight. Two refugees from the death and decay of London, Stevie Flint and Magnus McFall, have both washed up on the Orkney Islands. A rural community clinging to survival, the islands are home to a generation of youth who barely remember a time before the pandemic. One of them, Magnus' foster son, Shuggie, is fourteen years old and angry as hell: he and his young friends blame all adults for the loss of the technological and scientific wonders of the past.

When the foster parents of Shug's girlfriend, Misty, are found murdered and the young couple vanishes without a trace, Magnus fears the worst. Refusing to believe they could have committed the crime, and in order to find Shuggie and Misty before something terrible happens to them, Magnus and Stevie set off on a quest into the decaying city of Glasgow—and into the heart of a post-apocalyptic landscape they tried to leave behind when they fled the chaotic streets of London.