Shipwrecked, Daisaku (Johnny Sokko) and Juro Minami (an agent forUnicorn) drift to an island and are captured by the BF gang. The island is in fact, a base of the B.F. gang. They happen to discover a huge robot while they are running away. Giant Robot is being constructed by Dr. Gartua who is aware of the wicked project to conquer the earth by the B.F. gang. Dr. Gartua explains that Giant Robot works by atomic energy and only obeys the person who gives the original order. When Dr. Gartua tries to destroy the robot, his lab is destroyed. From the ruins Giant Robot stands up. Daisaku speaks to it and it is decided that he is the one who can control it.
