Once every year in the 215t century, the citizens of Earth celebrate Memory Day. On that day, they honor the memories of family members who have traveled so far into the universe that they are gone for years at a time! Some true pioneers have journeyed to galaxies so distant that they may never see their families again. In their honor, relatives on Earth build a robot in the likeness of the absent hero. The robot lives with the family as the hero himself, and is duly honored on Memory Day. Astro Boy volunteers to double as the robot of a little boy to help one family celebrate Memory Day. Once in the home, however, Astro Boy discovers that the missing little boy has actually disappeared by accident in a home-made Time Machine! Furthermore, the boy’s brother is mixed up with a gang of notorious criminals! Saving the brother from the fury of the mob and rescuing the little boy from the limbo of Time Forgotten becomes a double-barreled and almost insurmountable assignment even for Astro Boy!