Earthlight is a science fiction adventure story set on the Moon, where a government agent is looking for a suspected spy at a major observatory on the Moon. The context is strong tension between Earth (which controls the Moon) and independent settlers elsewhere in the Solar System. The year is not given, but it is some time in the 22nd century. There have been no wars for the last 200 years.

The time: 200 years after man's first landing on the Moon. There are permanent populations established on the Moon, Venus and Mars. Outer space inhabitants have formed a new political entity, the Federation, and between the Federation and Earth a growing rivalry has developed. EARTHLIGHT is the story of this emerging conflict.