Continuing his equatorial journey, Gordon Buchanan crosses the Pacific. This rich source of life is under pressure from rising temperatures, pollution and overfishing. In the Galapagos Islands, Gordon sees how drones are helping protect baby hammerhead sharks, and the iconic giant tortoise. On the other side of the Pacific, an aerial view sheds light on world’s richest marine habitats, and Gordon joins the search for clues about the future of our coral reefs in a mysterious tropical lake.