A family tries to escape an environmental holocaust.

Environmental pollution turns a normally harmless virus into an uncontrollable plague that is deadly to crops, and famine spreads throughout Britain. Biochemist Roger Burnham convinces his friend John Custance that Custance and his family must leave London immediately. On the way to the well-stocked farm owned by Custance's brother, they stop to steal firearms from a supermarket. The shopkeeper tries to stop them, but hoodlum Andrew Pirrie, who with his wife, Clara, has joined the party, shoots the man, and the group escape. Later, Custance's party is attacked by a band of motorcyclists who steal their cars and supplies and rape Custance's wife, Ann, and their daughter Mary. When they finally camp for the night, Clara attempts to seduce John, but the outraged Pirrie shoots her. Continuing on foot the next morning, they join another escaping group and finally reach the farm. John's brother David is unwilling to permit such a large number of people on his farm, however, and John, unwilling to abandon the rest of the people, leads an attack on the farm. David and many others are killed; the Custances and other survivors take over the land, determined to live in peace.