Once a talented scientist, Dr. Salvator, saved a little boy’s life by transplanting a shark’s gills in his body. Since then, Ichtiandr, as the scientist called his adopted son, became able to swim under water like a fish and dive at any depth, but it was hard for him to stay ashore for a long time. After years went by, rumors appear in a small sea town that there is a “sea devil”, a strange creature which frightens all the fishermen. At the same time a young man, who doesn’t communicate with people a lot and swims great, appears in the town. He meets a poor pearl diver’s daughter, a beautiful Gutiera, and falls in love madly with her.