The plot of Charlie Higson's The Enemy reads like an inverted fairy tale: one day, everyone over the age of 16 starts getting sick. Some of them die early on, and others leave their families voluntarily to try to protect them. The unlucky ones become something else: boil-covered, dim-witted zombies whose only goal is to consume flesh.
The kids who are left behind face incredible odds against their survival. The older ones are responsible for eluding the zombies, taking care of the young ones, and finding food in a precarious world where there is little left of anything, including hope. The Enemy follows groups of kids in London-- particularly, the "Waitrose kids," so named for the supermarket that they have secured and defended for the last year. They are lead by Arran, a natural leader who is both sensitive and fearless; defended by the gifted fighter Achilleus; and kept peaceful by Maxine, the second in command. But their resources are running low, and "the grown-ups" (their name for the zombies) are becoming more daring, picking them off one at a time.
One day a strange boy in a multicolored coat appears at their gate, bringing them tales of a peaceful life that another group of kids has made for themselves at Buckingham Palace. Allegedly, the kids live in security, where they are well-fed by the fruits of their own garden. He invites the Waitrose kids to join them, and they decide to embark on the dangerous journey from Waitrose to Buckingham Palace.