The Place: Mars, during the terra-forming process. As soon as Detective Ross Sylibus arrived at the spaceport, he got involved in a murder, The victim was Kelly McCanon, the popular singer. Ross discovered something shocking: the fact that the was not a human, but a "Third", a much more advanced robot than the corpse "Seconds" which are currently in common use. Ross must team up with Armitage of the Martian Police Department (MPD) to chase the killer, Rene D'anclaude, who is destroying the "Thirds" one by one.

Another Victim brings new confusion to the MPD, Still echoed by Danclaude's mocking laughter. And now, Armitage's mysterious disappearance places her under immediate suspicion.

After discontinuing the Third serial murders case the MPI) begins investigating the random acts of terrorism by Seconds. Ross, who can't understand this decision, goes to the Shinoura Police Hospital to investigate D'anclaude. Meanwhile, Armitage found data from Asakura which shows a young Asakura and D'anclaude together in a picture. What is the secret hidden between them? The key to solving the mystery is held by D'anclaude who is sleeping at Shinoura.