It's a post-apocalyptic world, several years after whatever the cataclysmic event, which has in turn caused frequent quakes as further potential hazards. The world is gray and getting quickly grayer as more and more things die off. A man and his pre-teen son, who was born after the apocalypse, are currently on the road, their plan to walk to the coast and head south where the man hopes there will be a more hospitable environment in which to live. The man has taught his son that they are the "good people" who have fire in their hearts, which in combination largely means that they will not resort to cannibalism to survive. The man owns a pistol with two bullets remaining, which he will use for murder/suicide of him and his son if he feels that that is a better fate for them than life in the alternative. Food and fuel are for what everyone is looking. The man has taught his son to be suspect of everyone that they may meet, these strangers who, out of desperation, may not only try to ....
Cormac McCarthy (novel), Joe Penhall (screenplay)