As mankind strives to rebuild society in the wake of climate change, over-population and global food shortages, every day is a struggle for people like Sid and his younger sister Lo.

They are `runners'- people whose very survival the government has outlawed.

As they move west, trying to find family or somewhere they can call home, they must work out which of the people they meet on the way can be trusted, and which want to cut their adventure short.

Encountering people on both sides of the law, as well as those who seem to exist outside it, Sid and Lo make and lose friends as they fight for their lives and each other.