The underwater cameraman, Nuno Sá, and the scientific researcher, Jorge Fontes, join forces to try to unravel a secret that hides the small and peaceful island of Santa Maria, the only place in Europe where we can find a population of the largest fish in the world - the Whale shark. With the help of Marienses fishermen, they will try to find out why the gigantic sharks of this island live surrounded by an escort of thousands of tuna. By placing small cameras on the whale sharks, they discover that this is the only place in the world where whale sharks and tuna collaborate to feed on large schools of small fish. But as they descend by submarine towards the deep waters of the Azores, they will have an encounter that will change forever what we know about the life of the biggest fish in the world.