The piece begins with a few paragraphs of commentary by the narrator in which she assures the reader that the story she is about to tell is a true one, its details having been recounted to her by the people who actually lived it.

The story proper begins with a detailed description of the South American country in which the first part of the action takes place: Coramantien, the name given by the author to what is now called Ghana. Narration describes the family history of the King of Coramantien and his grandson Oroonoko, apprenticed to a commander of the King’s armies and achiever of his own substantial record of military success. Narration also describes Oronooko’s love for his mentor’s daughter Imoinda; the King’s simultaneous (and immoral) desire for her; the King’s efforts to keep her from Oroonoko; and Oroonoko’s determined efforts to evade the King’s security measures and be with Imoinda as both he and his beloved believe is meant to be. In this they are helped by a pair of the King’s rebellious servants, and eventually manage to consummate their love.

When the King finds out, he sells Imoinda into slavery, but he tells Oroonoko that she is dead. Oroonoko falls into despair and depression, but is eventually roused to battle by an attack from a neighboring kingdom. He defeats the invaders and returns to the King’s court, where he is celebrated as a hero.

Just as Oroonoko is slowly beginning to get over the loss of his beloved Imoinda, he is kidnapped into slavery by an unscrupulous slave trader. Upon arrival at the plantation where he is to serve, however, Oroonoko is renamed Caesar. He is then recognized as a prince and as a man of exceptional value by the plantation’s owner, Mr. Trefry; and then recognizes another of Trefry’s slaves as Imoinda. Trefry, who had been attracted to Imoinda himself, allows them to continue their relationship, and also to escape being treated as slaves.

Sometime later, Imoinda becomes pregnant, and both she and Caesar (Oroonoko) become afraid that the child will be born into slavery. Caesar makes plans to lead a slave revolt and receives the support of the other slaves. As he leads them to freedom, they are pursued by the corrupt Deputy Governor Byam, who manipulates both Caesar and Trefry into believing that Caesar will be pardoned for what he has done. After Caesar lays down his arms, however, he is arrested and imprisoned; separated from Imoinda and whipped.

As he recovers, Caesar becomes increasingly convinced that he, Imoinda, and their child are destined for a life of slavery and suffering. When he is well enough he resolves to take his revenge on the Deputy Governor by killing him, and also resolves to kill Imoinda (as well as her unborn child) and himself so that they will never be enslaved. When he shares his plan with Imoinda she happily agrees and allows herself to be killed by her beloved. Caesar’s attempt to kill himself is interrupted by the Deputy Governor and his allies, who take him prisoner, then torture and kill him.

The story ends with the narrator’s comment that she hopes that in telling their story, the nobility and love of Oroonoko and Imoinda will survive “to all ages”.