Johnny Depp and Kate Winslet narrate an exploration of the exotic and rarely seen ecosystems that thrive in the deepest sections of the ocean. Divers photograph the most colorful undersea life, highlighting the symbiosis and biological traits these undersea creatures have developed to survive at such depths. Turtles gather algae to clean their shells, giant squid rapidly change color and divers witness the yearly spawning of a coral reef in the Gulf of Mexico.