Just prior to his release from prison, Ted Evans receives a threat from the man whose family he killed in a DUI - 'if you make contact with your family, I'll kill them'. Believing that the danger is real, Ted exiles himself to a reclusive life to protect his family. However, Ted's wife Sara knows the threat is merely a manifestation of her husband's profound guilt. Determined to rebuild their family, Sara tracks Ted down to confront him with hard evidence that the threat is imagined. But she has no idea just how unhinged he has become - or how real the threat may be.

More than seven years after the world has become a frozen wasteland, the remnants of humanity inhabit a gigantic, perpetually-moving train that circles the globe as class warfare, social injustice and the politics of survival play out.