Citizen of the Galaxy is a science fiction novel by Robert A. Heinlein published in 1957.

Thorby is a slave being sold on a strange planet. He is bought by a beggar for two minims and taken to an underground hideout -- which is surprisingly well-furnished. Gradually Thorby realizes that his new master is more than a beggar -- he's a spy!

The old man drills Thorby in mathematics, history and several languages including Galacta and English. He sends him on errands all around the Sargon's capital city, passing messages to starship captains and helping keep track of the comings and goings of ships involved in the slave trade.

One day, coming back from an errand gone awry Thorby finds out that the old man is dead, his head impaled on a pike with a defiant grin for the authorities. Mastering his funk, he evades the cops and seeks the help of a lady innkeeper who disguises herself as a rich dowager and smuggles Thorby into the spaceport. A friendly starship captain peels Thorby out of a pile of narcotic leaves and welcomes him aboard the ship of a Free Trader.