Isaac Asimov

Fearing a violent confrontation between Earthmen and Spacers, Detective Baley and his new partner, a robot, investigate the murder of a Spacetown scientist.

In the year 2100, mankind on Earth, settlers in a lunar colony, and aliens from the para-universe (a strange universe parallel in time to our own) face a race against time as they try to prevent the total destruction of the Earth by the invention of an Inter-Universe Electron Pump.