Roxana (a nickname given to her later in life) is born in France, and moves to England with her parents as a child. She grows up well-off and happy in London; at fifteen, she marries the son of a wealthy brewer. Roxana and her husband have five children together (two sons and three daughters), but her husband turns out to be selfish, stupid, and terrible at managing money. He gradually loses all of their money; one day, about seven years after their marriage, he vanishes while out hunting. Roxana is now destitute, and has no way to provide for herself, or her children. Roxana's maidservant, Amy, is very loyal and cunning, and finally persuades Roxana that she will need to give up her children. Amy forces the children's paternal aunt and uncle to reluctantly assume responsibility for the children. Amy also notices that the landlord who owns the house where Roxana has been living is interested in her, and encourages Roxana to become his mistress in exchange for economic support. Roxana is very hesitant at first, but after the Landlord promises to treat her as his wife and signs a contract providing her with money upon his death, the two of them become lovers.
Eighteen months pass; after Amy teases her, Roxana forces her to sleep with the Landlord. Amy becomes pregnant and gives birth to a daughter, whom Roxana provides for. Eventually, Roxana has two children of her own with the Landlord: a daughter who dies shortly after birth, and a son. After the birth of their son, the Landlord is required to go to France for his business as a jewel merchant, and Roxana goes with him, leaving Amy in charge of their house. While in France, the Landlord/Jeweller is murdered during an attempted robbery. Because Roxana had a premonition that he might be attacked, he had left all of his valuables (including some jewels) with her, but Roxana lets people think that he was robbed of these jewels so that she can keep them for herself. Roxana also cleverly manages to secure a lot of money and property from the Jeweller's estate, leaving her a very wealthy woman. A short time later, she attracts the attention of a German Prince and becomes his mistress. Roxana lives with him in France, and also joins him on an extended trip through Italy, during which time he buys her a Turkish costume. By chance, Roxana crosses paths with her first husband, who is now acting as a soldier in the French army, but she avoids him detecting her. During her relationship with the Prince, Roxana gives birth to three sons, two of whom survive. However, when his virtuous wife dies, the Prince begins to feel very guilty, and breaks off the affair.
Roxana decides to return to England, but needs help with moving her money and assets. She works with a Dutch merchant working in Paris who helps to make all of the arrangements for her, including liquidating the valuable jewels Roxana acquired when the Landlord/Jeweller died. However, a Jewish buyer recognizes the jewels, and suspects Roxana of theft or even murder. Roxana presents herself as a widow who is being unfairly persecuted, and the Dutch Merchant arranges for her to flee to Rotterdam while he takes care of the rest of her business. Amy and Roxana sail from France, but are caught in a terrible storm and end up landing in England. After a brief stay, Roxana carries on to Holland where she spends several months sorting out her financial interests. She is joined there by the Merchant, who begins courting her. Roxana begins sleeping with him, but shocks him by refusing to marry him, even after finding out she is pregnant. The Merchant is very saddened, but Roxana stubbornly returns to England with all of her wealth.
After giving birth to her final child, a boy, Roxana settles with Amy in Pall Mall, close to Buckingham Palace. She makes wise investments with her money and becomes famous for her parties, her outlandish Turkish robes, and the way in which she dances. This is when she earns the name "Roxana." She has affairs with important and wealthy men, including possibly the King himself, but ends up in an unhappy relationship with an old lord. Roxana also arranges for Amy to find out what happened to her children from her first marriage. She learns that two of them, one boy and one girl, have died; the other boy is working as an apprentice, and the two girls are working as servants somewhere. Acting on Roxana's behalf, Amy finds the boy, and provides a lot of money for his future education, so that he can eventually be a merchant. Through an incredible coincidence, Amy also realizes that one of the daughters is actually a servant in Roxana's own household. To avoid detection, Amy sends the daughter, Susan, away but also arranges for her to receive money and an education.
The experience of tracking down her children, as well as her unhappy relationship with the lord, leads Roxana to decide that she wants to change her life. She moves in with a Quaker landlady and lives a modest and quiet life, but finds herself unable to stop thinking about the Dutch Merchant. Eventually, Roxana sends Amy to France to find out news of him; while Amy is away, Roxana happens to run into the Merchant, who is now living in London, by chance anyways. After further hesitation, securing her financial independence, and the Merchant promising to make her a Countess by buying a title, Roxana and the Merchant finally marry. They are living happily together and planning to move to Holland when a problem arises. Susan, Roxana's daughter, has put together a lot of pieces about why she and her siblings mysteriously received money, as well as the circumstances around her mother's disappearance, the Jeweller/Landlord, and the glamorous Lady Roxana in whose household she worked. Susan thinks Amy (who passes herself off as a wealthy lady) is her mother, and is insistent on making her admit it. This risk of discovery is very worrying to both Amy and Roxana, and Amy suggests murdering Susan. Roxana is horrified by this suggestion, but Susan grows increasingly persistent in trying to find her mother, leading Roxana to go into hiding. Eventually, Susan vanishes, and Roxana becomes convinced that Amy did in fact murder her. Although Roxana and her husband try to have a happy life in Holland, the novel ends with a hint that Roxana ends up being punished for her crimes, and loses all of the wealth and happiness she has found for herself.