The Known World begins with the death of Henry Townsend. Once a slave himself, Henry dies a powerful slaveowner leaving fifty acres of land and thirty-three slaves behind.
Henry's father, Augustus bought his and his family's freedom from William Robbins, their slaveowner. Whilst Henry was still one of Robbins' slaves, he came to recognize and want power and money. He sold shoes and boots for years, saving and accumulating all the money he earned. Once he had enough, Henry began buying slaves and plots of land.
The first slave Henry bought was a man called Moses, a cruel and callous man, who he appointed as the overseer of his property and slaves. Being quite fond of Henry, Robbins instructs him on the methods of keeping slaves and the complexities of being a master. He instructs him on the importance of drawing a distinct master-slave relationship. To further equip Henry, Robbins encourages him to attend the school for free blacks. At the school, his teacher invites him to supper at his house where he meets Caladonia. After a short courtship the two get married and live rather happily until Henry dies.
Overcome and grief-stricken after Henry's death, Caladonia is unable to manage the estate. Overwhelmed by all her new duties she briefly sought comfort in Moses. Moses misunderstands their brief affair and takes it that Caladonia will soon free him and marry him. He quickly sends his wife and children away, promising that he will soon join them. However, a couple of days later Caladonia eliminates the misunderstanding, making it clear to Moses that she has no plans to marry him or set him free. Moses is violently ousted from the Townsend house.
John Skiffington is made aware of the missing slaves. Skiffington immediately suspects Moses of having been behind the disappearances. Fearing for his dream of freedom, Moses runs away from the Townsend estate and takes shelter in Mildred, Henry's mother's, house. Skiffington comes looking for Moses at Mildred's house where she refuses to surrender him. Both Skiffington and Milred are killed in the ensuing brawl. Moses was shot at and left injured during the confrontation and he is carried back to the Townsend estate where he lives in slavery for the rest of his life.
All of Robbins' children, both white and mixed, come down to visit him when he suffers a heart attack. Caladonia meets Louis Cartright, Robbins' mixed son, and the two marry and live on the Townsend estate. The book ends at the cusp of the Civil War, holding the hope of freedom for all those bonded slaves.
