Tristan and Vanessa journey to remote and magnificent Cocos Island -- the world's largest uninhabited island. Located off the coast of Costa Rica, Cocos Island offers dramatic and unparalleled beauty, including mountain ranges, lush tropical gardens and hundreds of cascading waterfalls. Tristan and Vanessa’s mission takes place in the seas surrounding the island. Diving into these waters is guaranteed to elevate the heartbeat. High-voltage, adrenaline-pumping action results when Tristan and Vanessa drop into the water to film schooling hammerhead sharks. They record this extraordinary yearly event, when hundreds of sharks appear out of the vastness of the Pacific Ocean to congregate off the island.

From a high-tech, live-aboard boat armed with expert crew, Vanessa and Tristan dive among hundreds of white-tipped sharks, huge manta rays, pods of dolphins, vast schools of jacks and awesome hammerheads. Tristan works for the first time with a rebreather – a piece of diving equipment that allows him to stay underwater longer, thus increasing his chances of witnessing marine life. But to Tristan’s frustration, his scuba gear hinders his access. Tristan and Vanessa switch to a mini-sub to follow the sharks into the deep. There they find just what they are looking for – vast groups of schooling hammerheads!

Back on dry land, Tristan and Vanessa unexpectedly run into a Costa Rican fishing boat and get insight into surviving as fishermen. Unfortunately, some hammerhead sharks fall victim to indiscriminate fishing practices. Tristan and Vanessa showcase the plight of the species, whose numbers are in decline.