Humanoid aliens have conquered the Earth. They are a highly advanced, peace-loving people with a secret agenda. Our hero is one of the invaders who has been surgically modified to pass for human. His mission is to infiltrate the human resistance and act as an agent provocateur to end racism by creating a common enemy. This clever take on McCarthy-era fear of brainwashing and communist spies would have made a good Twilight Zone episode.
The cover price on the April 1951 issue of Galaxy, in which Inside Earth was a featured novella, was 25 cents. It is now free on Project Gutenberg. ( )

After conquering Earth, the Valgolian Empire sends an undercover agent to foment rebellion against the Valgolians in the hope that humans will cast aside their chauvinisms (racism, ethnocentrism, nationalism, etc.) and unite as one planet. Only then will Earth be eligible to join the Empire as a member world and the Valgolians' work will be complete.

Although the characters lack depth, and the plot is a familiar one in the espionage genre, Anderson's concept raises SF to that higher level that the genre achieves so well when it challenges the reader's beliefs and prejudices. The portrayal of an empire exceptionally altruistic in its goals was also unique. ( )