Earthquakes killed more than a million people over the last century, and researchers fear that number could climb tenfold in the next one, not because the ground shakes harder but because so many more people now live in vulnerable mega-cities. This episode of Naked Science looks at the seismic risk facing sprawling urban populations, where collapsing buildings, not the tremors themselves, do most of the killing. Scientists and engineers explain the tools being built to see the threat coming: networks of seismic sensors that register the faintest tremor and computer models that simulate how a major quake would tear through a specific city's infrastructure. The film weighs how close any of this gets to actual prediction, telling us when and where a quake will strike, against the harder truth that early warning and better construction may be the more realistic goals. It closes without a tidy resolution, framing earthquake readiness as a race between growing cities and the science trying to keep pace with them.