Brain is the world's greatest computer, and also the most intelligent being on planet Earth. One day, Brain decides to abandon its terrestrial moorings, and it's up to The Defenders to track it down. Unfortunately, Brain has developed an amazing army of deadly giant robots, including one with a huge "17" emblazoned on its chest-plate, with which it plans to subjugate its creators. A young boy whose family was killed by Brain's followers manages to activate Daitetsujin 17, which thereafter comes to his rescue whenever he is in danger from Brain's minions.

A Southern California kid named Calvin Fuller is magically transported to the medieval kingdom of Camelot through a crack in the ground caused by an earthquake. Once there, he learns he was summoned by the wizard Merlin, who needs Calvin to save Camelot. Using dazzling modern inventions, can Calvin help King Arthur retain his crown and thwart the evil Lord Belasco?