Marine biologist and cameraman Rick Rosenthal has been filming in the ocean for decades. But one spectacle has eluded him and every other filmmaker, until now - the vast ”vertical migration”, when billions of animals rise from the depths to the ocean’s surface. It is the greatest migration on earth, and this astonishing event happens every night, in every ocean of the world. Limited camera and lighting technology have previously prevented the filming of this dramatic ocean event. Now for the first time, Rick will capture it on camera. But to do so he must risk the dangers and face the challenges of filming in the open ocean, in the dark. When he succeeds, Rick unlocks the secrets of a bizarre and alien world - a world driven by survival to remain forever in the shadows.