Eight years after the catastrophic downfall of the cult his sister Izzy had joined, Marc Winters has at last found a refuge from unwanted attention. The wildlife ranger of a small, unremarkable island, he's quietly helping to preserve what survives of nature in a world wracked by climate change and chaotic weather, and trying his best to put his past behind him.

But then his narrowboat is burgled, the counterterrorism police come calling, and everything he thought he knew about the cult and his sister's fate is turned upside down. A cabal of so-called deep dreamers has revived the cult's crazy belief that the world could be healed by collective dreams fuelled by psychotropic mushrooms. They appear to think that Winters possesses information crucial to their success, and when he tries to discover more about them, he becomes inextricably entangled in plans that challenge his very existence.