Shotaro Kaneda, fils du professeur Kaneda qui travaillait à la création de robots géants durant la Seconde Guerre mondiale, mène une enquête après que des criminels aient volé dans le laboratoire détruit de son père, les robots numéros 26 et 27, pour les utiliser à mauvais escient.Shotaro va alors découvrir le robot numéro 28, plus puissant que les précédents. Avec l'aide du professeur Shikishima, un ancien collègue de son père, tous les deux décident de faire en sorte que ce robot, renommé Tetsujin, devienne un allié de la lutte contre le mal.

By 2030, Shotaro's son was in charge of Tetsujin-28. An Interpol agent like his father, he used the aged robot to combat the Pink Mafia and the Franken organization.

At the beginning of the 21st century, scientists found that with new computers and super alloys, they could build an even bigger, faster Gigantor. They built the new Gigantor!

Professor Kaneda creates the ultimate soldier robot, Tetsujin, as a substitute for his son, Shotaro, whom he mistakenly believed died in a bomb raid on Tokyo during World War II. To prevent the army from using Tetsujin as a tool for destruction, the professor hides the robot on a remote island. Ten years after the war, Tetsujin is finally resurrected after 28 attempts made by the late Professor Kaneda's protege, Professor Shikishima. Meanwhile, Shotaro has grown up to become a genius boy detective and now joins forces with his beloved Tetsujin to wage a courageous battle against evil!