World's Busiest Cities

The team heads to Hong Kong, where space is at a premium and real estate is the most expensive in the world. They reveal the delicate daily balancing act that keeps the planet's most vertical city on track.

The team is in Mexico City uncovering the hidden systems and armies of people who run the sprawling megalopolis. They explore the city's waste management system and the daily struggle for clean, affordable drinking water.

The team heads to Moscow, a metropolis of 13 million people who like to play by their own rules. They reveal how a city forged by power and politics reconciles its communist past with its capitalist present.

The team is in Delhi, capital of India with a population of 26 million and rising. They reveal how the ever-expanding city feeds itself and how its people live, thrive and survive in their hot and hectic home.