Seen from the sky, the Earth is blue, the color of the sea. But what do we actually know about oceans ? What exactly lives in the oceans? To answer these questions, a team of scientists set sail aboard the schooner Tara. Their voyage will soon turn to an investigation into a secret realm... the largely unknown world of plankton. As we go deeper in the ocean, we're entering their secret world and explore the major role they are playing in the life of planet Earth.