A humpback whale travels from Antarctica to the coasts of the Colombian Pacific to give birth to its calf, but is threatened by a whale hunting ship that is sailing through the area and has managed to escape from the authorities. At the same time, Simón, Juana, Isabel and Lucas, accompanied by Aunt Abigaíl, arrive at Gorgona Island to embark on a submarine in the company of a famous scientist who studies the hearts of whales. Little do the boys imagine what awaits them on board and the dangers they will have to face to escape the persecution of the pirate whalers who want to catch their prey at any cost.