Sky City is the showpiece of civilisation on Earth in the 453rd century, a floating city in the sky! As the Tenth Doctor gives Heather a guided tour, he points out the old New Eurozone, which was destroyed in the Genetic Soil Wars. The Doctor explains to Heather about the high taxes people pay to live in Sky City because of the expensive anti-gravity generator it uses. They are knocked over by a man who passes Heather an egg-shaped object which the pursuing city police (the Cops), believe to be proof that she is another wanted associate of the Anti-Antigravity Activist organisation.