We screwed the world up so badly that not only were half the cities destroyed in wars, the rest were being threatened by earthquakes, floods, and other natural disasters caused by global warming, too many nuclear bombs disrupting the Earth’s crust, etc. So they put the cities on giant tracks/wheels/rafts. The cities consume a lot of fuel and raw materials, but the Earth’s pretty well tapped out. So the big cities prey on the little cities which prey on the towns. The Earth has settled down since then, but most of the cities are still moving and exist in a fragile stalemate with the Anti-Traction League of cities that stopped moving.
Tom grew up on a rather pseudo-Victorian London, wanting nothing more than to become a member of the Guild of Historians, and just maybe have an adventure and rescue a beautiful girl. Instead, he’s pushed off the city with a very ugly, scarred girl and learns that adventures are rarely so fun as they’re made out to be.
I’d prefer the premise if they just let it be steampunk, but the futuristic/post-apocalyptic setting made it harder for me to suspend disbelief. The adults are, by and large, fairly shallow, and one of them has a final redemptive moment that’s awfully unbelievable. But the setting is nifty, and it actually takes some pretty big risks.