More than 50 million years ago, the ancestors of the Whales and other Cetaceans returned to the ocean. This might seem like a backward step: how could a mammal breathe, give birth, suckle its young, sleep and feed underwater? Nonetheless, they succeeded in conquering the depths of the whole planet. To survive, they developed mysterious means of communication and new hunting techniques.Whale song, tail-slapping by Sperm Whales, Dolphins whistling: what are these giants of the deep saying through these enigmatic sounds? How do the Orcas of the Valdes Peninsula learn to beach themselves to catch prey, the only Whales to have mastered this technique? Such behaviors remain fascinating mysteries, and our quest to unravel them takes us from Polynesia to Florida, from Mexico to Argentina.Thanks to recent discoveries, and in the company of François Sarano, oceanographer and former companion of Jacques Cousteau, we discover these giants of the oceans and the secrets to their survival.