The open ocean, a realm of vast and powerful forces. Home to the largest animals on our planet. Far from land, and thousands of meters deep, its limitless blue punctuated by bursts of frenzied action. But at night, the open ocean changes. Billions of animals rise from the deep, strange new creatures, animals that thrive in impenetrable dark. This is the greatest migration on earth. Now one man plans to do what no man has done before. He will enter a strange and dangerous nighttime world, and attempt to film this epic movement of animals by immersing himself in it as it happens. His aim, to unlock the secrets of the great migration. The secrets of the dark side of the ocean.