Across the planet carnivores are struggling to compete in a world with a rocketing human population, but one predator is bucking the trend - the fox. Its numbers are increasing and its geographical range expanding. Chris Packham explores the secrets to its success - its senses, its intelligence and its flexibility. New research reveals how its slit pupils enables it to hunt in the bright desert day; how it may be using the Earth's magnetic field to determine the location of prey during a pounce; and how regular exposure to rotting food is improving the health of the red fox, enabling it to hold its own in an increasingly urban landscape.