Rule number one: Always be prepared . . .

Billy's mum isn't like other mums. All she wants is to teach him the Rules of Survival - how to make fire, build shelter and find food. She likes to test Billy on the rules until one day she goes too far, and Billy is sent to live with a dad he barely knows.

Then the world changes forever as people begin to be infected with a mysterious virus that turns their skin grey. As chaos breaks out, Billy has to flee the city. Suddenly he realises that this is what his mum was preparing him for - not just to save his family, but to save the whole world.