A castaway, Diego de Columba of Cordoba, is picked up by Captain Velasque and his ship. He tells a tale of how he was rescued by a man-sized sea creature (aka Sea Devil), after being washed up on a beach when pirates raided his ship and taking no prisoners. The sea creature was a scientist. It took him in, looked after him and became his friend. One day he returned to find that the pirates had anchored and had captured his friend. Not knowing what to do, Diego pressed a button on a small box the sea creature carried around, although it was forbidden to him. Another creature arose from the sea and destroyed the ship.