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.

Events are low-key: the government agent is a mild-mannered accountant who does not like the task. He notices the beauty of the Moon under 'earthlight'; the Earth in the sky far bigger than the Moon in the skies of Earth.

The story proceeds with very few violent incidents, though it does climax in a space battle. There is also an enigma - the apparent sighting of a 'beam of light', that should not be possible on the airless world. This is explained later in the story as a?weapons beam that included metal particulates moving at high velocity.

Even though many of Clarke's science fiction novels take place in rather similar futures—Earthlight,?A Fall of Moondust,?The Sands of Mars,?Rendezvous with Rama—the human background is never quite the same and they do not form a series.