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.

Young orphan Saburo uses a special helmet to command the Iron Robot 17 against the forces of the renegade computer Brain. Theatrical release re-edited from the first two episodes of the TV series, which actually preceded the original broadcast of the second episode.