As the novel begins, we are introduced to our protagonist Aminata Diallo, an 11 year old girl from Nigeria. She is kidnapped by a gang of slave traders along with a number of others form her village and is forced to walk alongside them for 3 whole months all the way to the docks where she is to be sent to be America. During her journey, she encounters a boy of about her age, Chekura, whom she manages to find a friend in. They are both sent to America to be sold to slave owners, but are separated upon their arrival. It is not known what happens to Chekura but Aminata is sold to a South Carolinian plantation owner by the name of Appleby. During her stint working for Appleby, Aminata makes friends with Georgia, a fellow slave who teaches Aminata English. She also picks up reading and writing from another fellow slave Mamed, although she learns this in secret to avoid punishment from Appleby.
Years pass and Aminata is now a teenager. During this time, she miraculously reunites with Chekura and the pair fall in love. Much to the chagrin of Appleby, Aminata slips out of the plantation to meet with Chekura regularly and is reprimanded by Appleby who rapes her as punishment. In spite of this, Aminata and Chekura are secretly wed and they have a child whom they name Mamadu. This further enrages Appleby, who orchestrates the separation of Aminata and her son by selling them to different owners. Aminata is sold to a Jewish man named Solomon Lindo, who moves with her to Charles Town.
In a surprising turn of events, Lindo and his wife accord Aminata a level of freedom, allowing her to read and write openly, causing Aminata to slowly grow close to the Lindos. However, not long after Aminata begins working for the Lindos, Lindo's wife and child are killed by a smallpox outbreak. Chekura reappears and reveals that Lindo was partly responsible for Appleby's plot to separate Aminata and Mamadu. This angers Aminata, who becomes cold towards Lindo. Lindo, in an attempt to restore the relationship between the two, opts to relocate with Aminata to New York. The Revolutionary War soon breaks out, harkening a period of great turmoil during which Aminata is able to escape from slavey and work as a midwife and an English teacher, aiding the British.
After the war, her fluency in English is discovered and she aids in the recording of names into the Book of Negroes, a list of black slaves freed during the war who sought to leave the newly independent United States. During this time, she yet again reunites with Chekura and the pair agree to leave for Nova Scotia to resettle and begin a new life. Just as they are about to leave on a ship, there is a hiccup and Aminata is arrested under Appleby's accusation of her being an illegally escaped slave. However, she is saved when Lindo appears at her trial to vindicate and free her.
Aminata arrives in Shelburne where she begins work for various wealthy white families. During this time, she gives birth to a second child, a daughter who she names May. She also later finds out that the ship her husband was on had sunk mid voyage and that Chekura had never made it to Chekura. However, within a few years, relations between the white and black communities of Shelburne turn sour and the Witherspoons, one of Aminata's former employers, abduct her daughter May.
A British Naval Officer Captain John Clarkson becomes cognizant of the souring of relations between the white and black communities. With Aminata's help, he manages to convince the black people to relocate to a new town in Sierra Leone with the aid of the British. However, the ironically named Freetown fails to provide safe harbor for the black people and this leads to Clarkson proposing Aminata be brought to Britain to speak out against slavery. Aminata initially refuses, but after a failed attempt to return to her village of birth due to her old age, she relents and joins Clarkson on a voyage back to Britain.
She becomes a widely known public figure in Britain who speaks publicly against slavery and publishes a memoir with the aid of Clarkson. In her old age, she is reunited with her daughter May, who it is revealed was able to escape and become a teacher. The novel ends with May taking care of Aminata in her final days.