Detective Al Bailey is invited to one of the outer worlds, Solaria, where a mysterious murder has occurred. Solaria is characterized by the isolation of its inhabitants from each other (even husbands and wives see each other on a schedule), which makes the murder all the more incredible. From childhood, people grow up surrounded by robots, and as adults, personal contact is considered inappropriate and a difficult challenge. The unpreparedness of the inhabitants for the murder leads them to accept the invitation to bring in an Earthling. Upon arriving on the planet, Al Bailey meets his old acquaintance, the robot Dan, and they begin their investigation together.