Gesicht, an android police detective of Europol, is tasked with finding the murderer of Montblanc, a retired war hero robot. Although it appears that only a robot could have committed this crime, the murder of a renowned robot rights activist casts doubts on the criminal's identity. Indeed, outside of an isolated and unexplained incident that occurred eight years ago, robots are programmed to be unable to kill human beings. However, the lack of human evidence on the crime scene and the similarity of modus operandi lead Gesicht to suspect that the two murderers might be the same being—be they man or robot.

Shortly after Montblanc's passing, another retired elite war robot is mysteriously eliminated. Gesicht notices a pattern in the choice of murder victim: both dead robots belonged to a group of the seven most powerful war machines ever designed. Determined to stop the murderer from eliminating the five remaining veterans, Gesicht seeks help from Atom, a cutting-edge android who resembles a human boy. The duo must now hunt down the rogue killer before the series of murders is carried on, lest the very fabric of society suffer irremediable damage.