Oroonoko chronicles the story of the African prince Oroonoko and his beloved wife Imoinda, who are captured by the British and brought to Surinam as slaves. The tale is set primarily in this locale on the northern coast of South America during the 1640s, just before the English surrendered the colony to the Dutch.
A young English woman, the nameless narrator, resides on Parham Plantation awaiting transportation back to England. She is the daughter of the new deputy-governor, who unfortunately died during the family's voyage to take up his new post. During her wait, she has the opportunity to meet and befriend prince Oroonoko and his lovely wife, Imoinda. Before introducing the primary character, however, the narrator provides great detail about the colony and the inhabitants, presenting first a list of multicolored birds, myriad insects, high-colored flora and exotic fauna, and then an almost anthropological account of the natives with whom the British trade and who seem to the narrator to be as innocent as Adam and Eve in "the first state of innocence, before man knew how to sin." The British, she insists, live happily with the natives. Because of their vast numbers, the colonists are unable to enslave them and so must look elsewhere for slaves to work on the sugar plantations--that is, they look to Africa.
After her overview of Surinam, the narrator switches the setting to Coramantien (today Ghana) on the west coast of Africa, where the protagonist Oroonoko is about to meet Imoinda, the daughter of the general who has just died saving Oroonoko's life. The king of Coramantien, who is the 100-year-old grandfather of Oroonoko, has also fallen in love with the young and beautiful girl and has beaten Oroonoko to the punch by sending her the royal veil, a gift Imoinda cannot refuse, and which signifies that she is now the wife of the king. She will spend the rest of her days locked within the otan, or the royal seraglio, which only the king can visit. Oroonoko, however, breaks into the otan with the help of his good friend Aboan, who keeps one of the king's senior wives named Onahal occupied with lovemaking. The king catches him, and Oroonoko flees. Although Imoinda is sold into slavery, the king later informs Oroonoko that she has been honorably put to death.
Meanwhile, the British arrive in Coramantien to trade for the war captives whom Oroonoko sells as slaves. The captain invites the prince and his friends to board his vessel as his guest, but then surprises them and takes them captive. Soon after he promises Oroonoko his freedom, when he and his friends refuse to eat, but he fails to keep this promise. Upon the ship's arrival at Surinam, Oroonoko is sold to the mild-mannered and witty overseer of Parham Plantation who befiends him, Mr. Trefry. At this point, Oroonoko meets the narrator. She and Trefry assure the prince that as soon as the lord-governor Willoughby arrives in Surinam he will be set free.
Because of his high social status, superior education, and spectacular physical appearance, Oroonoko is never sent to work. He resides away from the other slaves in the plantation house. While walking with Trefry one day, he sees Imoinda. The lovers fall happily into each other's arms and all but instantly marry. Soon Imoinda becomes pregnant.
At this point Oroonoko, who desperately desires that his child not be born a slave, becomes even more concerned about his enslaved status despite Trefry's and the narrator's renewed promises that all will be well when the governor arrives. They attempt to divert him with hunting, fishing, and a trip to a native village. Oroonoko is a champion hunter who kills two tigers singlehandedly in addition to managing to hold onto a fishing rod even when an electric eel knocks him unconscious. Although the native village provides distraction (and another means for Behn to provide cultural information about the natives in this region), Oroonoko incites a slave revolt with the other plantation slaves. They escape on Sunday night when the whites are drunk, but they leave a trail that is easy to follow because they have to burn the brush in front of them. The plan is to settle a new community near the shore and find a ship on which to return to Africa. Meanwhile, the narrator flees to safety, but later she gets a firsthand account of the events.
Deputy-governor Byam negotiates with Oroonoko to surrender and promises him amnesty. Once more he assures Oroonoko that he and his family will be freed and returned to Africa. Hardly surprising, however, Byam lies once more to Oroonoko and sees that he is whipped brutally, with pepper poured into his wounds, as soon as he surrenders. The despondent Oroonoko realizes he now will never be free and that his child will be born in captivity. He informs Imoinda that he has decided to kill her honorably, take revenge on Byam, and then kill himself. She thanks her husband for allowing her to die with dignity, and he cuts her throat and removes her face with his knife. But Oroonoko becomes prostrated with grief and can never generate enough energy to go after Byam. Sinking ever deeper into depression, he waits for eight days next to the body of his dead wife until the stench brings Byam's men to the site, where they immediately set about killing him. Finally, Oroonoko stands stoically smoking his pipe while they chop off his nose, ears, and one leg. Then he falls down dead, and they quarter his body before disposing of it.