Two-thirds of the planet is ocean, and most of it had never been filmed before the BBC crews behind this series went looking. David Attenborough narrates as cameras follow blue whales feeding off Baja California, sperm whales diving into the pitch-black midwater to hunt giant squid, and clouds of plankton triggering feeding frenzies that pull in sharks, tuna, and dolphins at once. Deep-sea submersibles reach hydrothermal vents where tube worms and blind shrimp survive on chemical energy instead of sunlight, and time-lapse photography turns coral reef spawning into a single overnight event. The series moves pole to pole and surface to trench, covering open ocean, coral seas, the deep, and frozen waters in turn, each episode built around one habitat and the animals that have adapted to its specific pressures, temperatures, and light. Footage of a coordinated dolphin and shark hunt, captured for the first time here, is the kind of scene the whole series was built to find.