During an investigation, private detective Shunsaku Ban and his nephew Kenichi travel from Japan to Metropolis—a restless high-tech city where people brutally persecute their robot cohabitants and a dictatorial force rises in power. The two are investigating Dr. Laughton, a scientist suspected of human organ trading, who is supposedly hiding there. Unbeknownst to all, Dr. Laughton has built a cutting-edge female android called Tima for the most influential man in Metropolis, Duke Red.

When Dr. Laughton's laboratory ends up in flames following an unforeseen incident, Shunsaku and Kenichi are separated while looking for survivors. Kenichi rescues a disoriented Tima and struggles to protect her from Duke Red's ruthless foster son, Rock, who pursues the robot girl. Unaware of Tima's true nature, Kenichi befriends her as a human being. Meanwhile, Shunsaku tries to reunite with the boy, unraveling dark schemes that evolve in the city's background—including the key role of Kenichi's protegee in Duke Red's ambitious goal for domination.