For as long as he could remember, young Thorby had been a slave—until he lands on Jubbal, one of the Nine Worlds of the Sargon Empire, and is purchased by a beggar named Baslim. It is not long before Thorby realizes that Baslim is no simple mendicant, but a spy and one who despises the slave trade. Once Baslim educates Thorby in reading, writing, mathematics, and even a bit of espionage, he frees Thorby from slavery and adopts him as his son.

In the event of his death, Baslim commands Thorby to carry a special message to the captain of the first Free Trader vessel that landed on Jubbal. Baslim uses hypnosis to allow Thorby to memorize the message in an unfamiliar language.

After Baslim is finally arrested and executed by Sargon police, Thorby makes his way to the spaceport where he approaches Captain Krausa of the Sisu and delivers the message. As it turns out, the Free Traders owe a special debt to Baslim and as such, Krausa follows the old man’s instructions and adopts Thorby into his family. Thorby becomes a crewman aboard the Sisu—but only temporarily, for Baslim also wished to have the Free Trader captain turn over Thorby to a Hegemonic military vessel where he would have the opportunity to discover his true lineage. Baslim suspected that Thorby had been abducted from a Terran family.

When Thorby is finally reunited with his family on Earth, he learns that he is heir to a fortune… but not everyone has his best interests at heart. Worse, the company once owned by his parents might now be indirectly involved in the same detestable institution from which Baslim had liberated him.

Citizen of the Galaxy is one of Heinlein’s juvenile SF adventure novels, what we would today categorize as young adult. It is a delightful “rags to riches” tale that allows the reader to experience a wide range of lifestyles and family structures through Thorby’s eyes as he evolves from slave to adopted family member of Free Traders to an enlisted man aboard a military vessel and finally, the head of one of the wealthiest corporations on Earth.