Mary Fitz-Allard visits her love Sebastian disguised as a seamstress. Formerly betrothed, their engagement was called off by Sebastian's father, Sir Alexander, who was not satisfied with the amount of the dowry. Sebastian tells Mary he must stay away from her for some time. She asks him why, thinking that he has taken another lover. He assures her that this is not the case, and that he intends to trick his father into letting him marry her. His plan is to convince his father that he has fallen madly in love with Moll, a girl with a reputation of being extremely unusual, who dresses in men's attire and has a reputation for behaving outrageously. He intends to horrify his father to such an extent that he lets him marry Mary, who would then seem a much better alternative compared to Moll. Mary agrees to this plan, and wishes him luck.
Sir Alexander invites guests to his home, among whom are Omnes, Laxton, Sir Davy, and Greenwit. When they begin to mock Moll, Sebastian declares his love for her. Offended, he storms out, humiliating his father. Ralph Trapdoor enters, and Sir Alexander calls him aside and hires him to get as close to Moll as possible and eventually kill her.
In town near various shops, Laxton tries to borrow money from Mistress Gallipot, a married apothecary. Laxton admits to Greenwit and Goshawk that he pretends to be attracted to her in order to get money, which he then spends on other women. Meanwhile, Jack Dapper shops for a feather from Mistress Tiltyard. At the seamstress shop, Mistress Openwork scolds Master Openwork when he offers to handle the noblewoman's smock she has been working on. Laxton sees Moll and offers to pay her for sex. They agree to meet at Gray's Inn Fields at three. Mistress Openwork refuses to sell anything to Moll and throws her out of her shop. Goshawk later tries to get Mistress Openwork to sleep with him by saying that her husband, Master Openwork, has been seeing a whore in the suburbs. Trapdoor sees Moll and tells her that he admires her and wants to offer his services as a servant.
Sebastian laments of his broken heart and says that a man should be free to marry whom he pleases. He says all this pretending not to notice that his father is hiding in the room, listening to him. Moll enters with a porter, and Sebastian, knowing his father is watching, declares his love to her. She tells him she has no intention to ever marry, which makes Sir Alexander feel relieved. A tailor enters and measures Moll for her breeches.
Laxton goes to the field, and gets impatient waiting for Moll, not seeing her there. Suddenly, a young man approaches him who he does not recognize at first, then realizes that the man is actually Moll. She pulls out her sword and defeats him in a fight, denouncing him for his lechery. Laxton confesses he has done wrong and leaves. Trapdoor tells Sir Alexander that Sebastian was seen with Moll, then continues to follow her. Master Gallipot unknowingly delivers a love letter from Laxton to Mistress Gallipot but then catches her reading it. When she is caught, she pretends that she and Laxton were formerly contracted to marry and that she must pay him money. Laxton eventually, at the hinting of Mistress Gallipot, understands her scheme and pretends that he will marry her at any cost. Laxton takes the money and calls women deceivers.
Sir Alexander goes to talk to Trapdoor, who reports to him that Moll has been meeting Sebastian dressed as a man. Sir Davy complains to Curtilax about his son Jack and how he must be punished.
Sir Alexander asks Trapdoor when Moll is going to meet Sebastian next so that he can trick her into stealing expensive items. While they are talking, Sebastian asks Moll to sing rather than fight and she does. He offers to pay her, most likely for playing along, but when his father enters, he covers it up by saying she is a musician and he is paying her for her songs.
Mistress Openwork and Mistress Gallipot talk. Openwork admits she knows what Goshawk is up to, and Gallipot says she knows what Laxton has been up to and has finally gotten rid of him too. When Laxton and Goshawk enter, Gallipot tells Laxton off. Mistress Openwork shouts at Master Openwork, accusing him of betraying her for a common whore, while Goshawk stands by nervously, telling Master Openwork she is not well. Master Openwork asks Goshawk if he knows who has been telling his wife that he was sleeping with another woman at Brainford. Goshawk says he doesn't know, to which Mistress Openwork tells him that it was indeed he who told her. Laxton comes back to ask for more money from Master Gallipot, and Mistress Gallipot tells him off once more. She is forced to explain to her husband what was really going on, but assures him that she and Laxton never really slept together. Laxton also tells Master Gallipot that he never meant to sleep with his wife, and that he will pay him back in full, plus interest.
Moll enters with Jack Dapper, Sir Beauteous, and Sir Thomas. She tells them that she knows what Trapdoor has been up to. Trapdoor enters disguised as a poor soldier with an eyepatch, along with Tearcat, also in disguise. Moll verbally abuses them and Trapdoor asks her how she can speak in such a way to a soldier. She calls them out on their disguise. Later, thieves try to approach Lord Noland and Omnes but Moll warns them. Knowing they have been caught, the pickpockets curse her and flee.
Sir Alexander continues to curse Moll, calling her a thief. He asks Sir Guy Allard, Mary's father to help him. Sir Guy however is still upset that he did not let his daughter marry Sebastian and says it's his own fault that things happened this way. Moll enters as a bride for Sebastian, and tells Sir Alexander that he should be happy to have a daughter-in-law that is as good a man as his son. Mary enters with Lord Noland and Sir Beauteous. Moll admits to Sir Alexander that she has played a part in tricking him. She said she did them a favor and that she herself would never marry. Sebastian apologizes to his father and says he always loved Mary. Sir Alexander is happy to hears this and gives Sebastian and Mary his blessings. He apologizes to Moll for speaking ill of her and confesses his faults. Finally, he calls everyone together to remember the happiness of this day.
