The most complex marine species on the planet, our counterparts in the sea, is the orca, the ruler of the ocean. Orcas, also called killer whales, are the most widely distributed marine mammal in the world — their realm extends from the Arctic to the Antarctic. They number fewer than 100,000 worldwide, and learning more about them is a global endeavor for Jean-Michel Cousteau and his team of explorers, who travel to both the Northern and Southern hemispheres as they seek out killer whales in the Atlantic and Pacific oceans. Cousteau and the team discover that people and orcas share surprising similarities, even similar needs, and they relate their findings to the captivity and release of Keiko, from Free Willy fame, who captured the world’s imagination and whose survival depended on pioneering efforts to reintroduce Keiko into the wild. The team also learns how some of the threats to killer whales now intersect with human lives. Intriguing detours in the expedition arise, leading to critical examinations of our environment, of the food on our dinner tables, even of our own health.