"Armitage III" is a four-episode OVA series set in a futuristic world where humans and robots coexist. The story takes place on Mars, a colonized planet where advanced robotics have become integral to society. The narrative centers around Ross Sylibus, a former Earth police officer who transfers to the Martian police force. He is partnered with Naomi Armitage, a skilled and enigmatic officer with a sharp attitude. Their partnership begins with the investigation of a series of murders targeting "Third-Type" robots, highly advanced androids indistinguishable from humans.

The murders reveal a deeper societal conflict. Third-Type robots, designed to mimic humans perfectly, face widespread prejudice and fear from both humans and less advanced robots. As Ross and Armitage delve into the case, they uncover a conspiracy involving powerful corporations and political figures who seek to eliminate the Third-Types to maintain control over Martian society. The investigation becomes increasingly personal for Armitage, as her own identity as a Third-Type is revealed, raising questions about her origins and purpose.

The series explores themes of identity, prejudice, and the ethical implications of artificial intelligence. Ross, initially skeptical of robots, develops a complex relationship with Armitage, challenging his preconceptions about humanity and technology. The narrative builds tension through a mix of action, mystery, and philosophical inquiry, culminating in a confrontation that forces both characters to confront their beliefs and the societal structures that perpetuate discrimination.

The main characters are Ross Sylibus, a grounded and pragmatic detective, and Naomi Armitage, a fiercely independent and resourceful officer whose true nature drives much of the story's conflict. Supporting characters include key figures in the conspiracy, such as corporate executives and government officials, as well as other members of the Martian police force who provide additional context for the societal tensions on Mars. The series balances its futuristic setting with a focus on character-driven drama, making it a notable entry in the cyberpunk genre.