Roughly 20 miles off the coast of west Africa, sits a volcanic relic now completely blanketed in equatorial rainforest: the island of Bioko. It's home to some very rare species, including the drill -- one of the most endangered primates in the world. Join us on a jungle expedition as we uncover the secret life of these reclusive primates and track down the seasonal migration of the goby -- a plucky fish battling its way upriver past strong currents, deadly predators, and even a 100-foot waterfall, to reach the spawning grounds of its youth.