One day, a talented scientist, Dr. Salvator, saved the life of a little boy by transplanting shark gills into him. From that day on, Ichthyander, as the scientist called his adopted son, could swim under water like a fish, dive to any depth, but it was hard for him to stay on land for a long time ... Years later, rumors spread around the quiet sea city about a strange creature that terrified on all fishermen about the "sea devil". At the same time, a young man appears in the city, who communicates little with people and swims well. He meets the daughter of a poor pearl diver, the beautiful Gutierre, and falls in love with her...