S1, E3: The ocean occupies more than two-thirds of our planet's surface, constituting an extreme habitat with dimensions beyond our comprehension and a variety of lifeforms that can scarcely be chronicled. It is in the seven seas that we find the last "white spaces" of our world: unexplored, mysterious expanses still virtually off-limits to human beings – although that doesn't stop us recklessly plundering and destroying these areas. Underwater film-maker Thomas Behrend, honoured with numerous awards for his work, has been travelling the world for many years on a mission to record the fantastic, teeming life of our oceans and establish the effects of human activity on the sensitive ecosystems. This time his mission is to capture on film molas and manatees, two giants of the oceans. This entails many months of filming, taking Thomas from the USA to Italy. On the Pacific coast of California, and just off the island of Elba in the Mediterranean, Thomas searches for a mysterious deep-sea dweller whose eccentric appearance has fascinated the film-maker since he was a boy. 3 metres in diameter, weighing up to 2 tons, the circular sunfish is one of the biggest and strangest bony fish to roam the oceans. Despite its enormous size, this creature, which dines off jellyfish, is very seldom seen, since its habitat is the open ocean. But there have been reports of sunfish sightings in shallow coastal waters, or near the surface of the sea. Thomas is determined to discover more about the curious wanderings of the colossal creatures. With the support of experts and the help of a remote-controlled camera submarine, he actually succeeds in tracking down the legendary fish and capturing footage that reveals unexpected insights into its behaviour.