- Act I
Sarah Millwood, a London prostitute, schemes to find some innocent young man "who, having never injured women, [would] apprehend no injury from them" (I.iii) to seduce and exploit for money. She observes young George Barnwell in town, and she invites him to her house for supper. She realizes that he works for the wealthy merchant Thorowgood (who is known throughout London for his wealth and success). She decides to seduce George Barnwell at supper with irresistible flattery, and he succumbs to her wiles in a way that will give her access to Thorowgood's money, and she manipulates Barnwell to steal from his boss.
- Act II
Upon returning home the next morning, George feels he has betrayed Thorowgood by disobeying his curfew. The guilt he feels from disobeying the rules of the house, as well as the guilt he feels from his fornication with Millwood, leaves George tormented. His guilt is compounded by the loyalty of his friend Trueman. Soon, Millwood visits George at his place of work. When she discovers he no longer wants anything to do with her, she begins to sense her money-making scheme has come to an end. She quickly thinks of a lie to tell George to keep her plan going. She tells George that the man who provides her with housing somehow found out about their tryst and is now evicting her because of it. This evokes new feelings of guilt from George, and he is prompted to steal a large sum of money from his employer's funds to give to her to amend the situation.
- Act III
After giving her the money, George feels unworthy of his kind master, Thorowgood, so he runs away and leaves a note for Trueman confessing his crime. Having no place to go, he turns to Millwood for help. At first she refuses him since his employer's money is no longer at his disposal, but she quickly remembers that he has previously mentioned a rich uncle. She again manipulates George into believing that she truly loves him, and concocts a scheme for him to rob his uncle. George objects, saying that his uncle will recognize him as his nephew; Millwood answers that the only way, then, will be to also murder his uncle. In a fit of passion, George runs off to commit the robbery and murder. He finds his Uncle Barnwell alone, and as he approaches, George veils his face and attacks his uncle with a knife. As he lies dying, Uncle Barnwell prays both for his nephew and his murderer, not knowing that they are the same. Overcome with sorrow, George reveals himself to his uncle, and before he dies, Uncle Barnwell forgives his murderous nephew.
- Act IV
In the meantime, Lucy came to Thorowgood and revealed the truth behind what Barnwell had done. Because of this Thorowgood rushes to exit and tells Lucy she must keep watch on Millwood's house. Later, George returns to Millwood's home upset, trembling, and with bloody hands. Upon realizing that he did not take any money or property, Millwood sends for the police and has George arrested for murder. Two of Millwood's servants, Lucy and Blunt, who were aware of the plan from the beginning, have her arrested as well. Both George and Millwood are sentenced to death. In the last scene of Act 4 Millwood expresses to Thorowgood that she is not remorseful in the least bit saying, "I hate you all! I know you, and expect no mercy -- nay, I ask for none. I have done nothing that I am sorry for. I followed my inclinations, and that the best of you does every day. All actions are alike natural and indifferent to man and beast who devour or are devoured as they meet with others weaker or stronger than themselves."
- Act V
Millwood blamed society and men for what she has become. She is not remorseful at all and with passion accepts her fate. Despite all that has transpired, George is visited by Thorowgood and Trueman in his prison cell. They console and forgive him. Thorowgood provides for his spiritual needs by arranging a visit from a clergyman. In the end, George is truly repentant for his sins and is at peace with himself, his friends, and God. Trueman ends the show with a small monologue saying, "In vain with bleeding hearts and weeping eyes we show a human gen'rous sense of others' woe, unless we mark what drew their ruin on, and, by avoiding that, prevent our own" (Act V Sc. X) to show that the play was to learn how to do the right things in our own lives.
