A merchant, accompanied by an officer of the law, threatens the goldsmith Angelo with arrest if he doesn't come up with the money Angelo owes him. Not to worry, Angelo says: Antipholus owes me the exact amount the merchant is demanding, and has promised to give it to him at five o'clock. The officer notices that Antipholus is coming their way now, but unfortunately it's Antipholus of Ephesus, who has no idea that Angelo has handed over the gold chain to Antipholus of Syracuse by mistake. Antipholus-E. is busy ordering Dromio-E. to go buy a length of rope that he plans to use as a whip on Adriana "and her confederates / For locking me out of my doors." As Antipholus notices that the goldsmith is there, Dromio hurries off on the errand.
Antipholus proceeds to chide Angelo for not delivering the chain to him at the Porpentine, but Angelo is determined to treat everything that he hears from this rather eccentric man as a joke -- as he did when he delivered the chain to Antipholus of Syracuse, who claimed to have no idea that he'd ever ordered a chain. So Angelo remarks on Antipholus-E.'s "merry humour" and asks him to pay for it now, since the merchant is in a hurry to get off to sea. "I am not furnish'd with the present money," Antipholus-E. replies, but if Angelo will take the chain to his house and ask Adriana for the money, everybody will be happy.
Fine, says Angelo. So give me the chain and I'll go to your house -- the merchant, after all, is in a hurry. Antipholus-E., who is already irritated because Angelo didn't bring the chain to him at the Porpentine, accuses Angelo of starting a fight over it. Angelo insists that he has already given Antipholus-E. the chain. Antipholus-E. is equally sure that he did no such thing. The merchant tries to intervene, and only confuses things further. Finally, the merchant orders the officer to arrest Angelo, and Angelo orders him to arrest Antipholus.
Dromio of Syracuse then walks into the middle of this melee to tell Antipholus-E. that he's arranged with the owner of a ship to take them to Epidamnum. Antipholus-E. says he sent him for a rope, not a ship, and promises to "teach your ears to list me with more heed," but first sends him to Adriana with a key to the desk in which "There is a purse of ducats; let her send it. / Tell her that I am arrested in the street, / And that shall bail me." Then he lets himself be taken off to prison, along with Angelo.
Dromio-S. certainly doesn't want to go back to Adriana's, for fear of encountering the globular Nell, but he obeys.
At Adriana's, she and Luciana are discussing Antipholus-S.'s attempt at wooing Luciana, who admits that he did so "With words that in an honest suit might move" -- a step toward hooking up Luciana with Antipholus-S. at play's end. Adriana denounces Antipholus, but when Luciana suggests she'd be better off without him, Adriana admits, "Ah, but I think him better than I say."
They are interrupted by Dromio-S., who is out of breath from having run to their house. (Perhaps a bit of theatrical humor directed at the obvious lack of distance from where we last saw Dromio on the stage.) He tells them that Antipholus has been arrested and needs the money from the desk as bail. Adriana sends her sister to fetch it, and dispatches Dromio to the jail with it.
Antipholus of Syracuse enters, meditating on the way everyone in Ephesus seems to know him, and more and more convinced that the place is full of witches and "Lapland sorcerers." And then Dromio of Syracuse arrives with the money to bail him (or rather, Antipholus of Ephesus) out of jail. They talk at cross-purposes until a courtesan from the Porpentine enters and notices that Antipholus-S. is wearing the chain that she was promised by Antipholus-E. Both Antipholus and Dromio become convinced that she's a "devil" or "the devil's dam" or "a sorceress." The courtesan thinks they're joking, but what she really wants is the ring that she gave to Antipholus-E. at dinner. Either that, she says, or the chain, but Antipholus replies, "Avaunt, thou witch," and he and Dromio hurry away.
The courtesan is convinced that Antipholus has gone mad, especially after the story he told at dinner about being shut out of his own house, so she decides to go to his house "And tell his wife that, being lunatic, / He rush'd into my house and took perforce / My ring away."
Antipholus of Ephesus is being escorted by the officer when he sees Dromio of Ephesus arriving, he thinks, with the money. Dromio, of course, knows nothing about this errand: He has brought the rope he was ordered to fetch. When he thinks that Dromio has spent the bail money for the rope, he starts to beat Dromio. Then Adriana, Luciana and the courtesan, accompanied by a schoolmaster named Pinch whom they have enlisted to try to break the spell of madness they believe Antipholus to be under. Pinch asks for Antipholus's hand so he can feel his pulse, but Antipholus replies, "There is my hand, and let it feel your ear," and hits him.
Pinch begins an invocation to try to expel the devil from Antipholus, who turns on Adriana and asks if Pinch was the one who dined with her while he was shut out of the house. Adriana insists that Antipholus dined with her, so he asks Dromio whether he was locked out of the house. Dromio confirms that indeed he was, and that the kitchen-maid aided in shutting him out. (Foakes takes this as evidence that Luce and Nell are the same person. Not that it matters.) But when Adriana insists that she gave Dromio the money to bail Antipholus out of jail, Dromio denies it, swearing that the only thing he was sent for was a rope. At this, both Antipholus and Adriana turn on Dromio.
Pinch insists that both Antipholus and Dromio are mad and "must be bound and laid in some dark room." Finally, Antipholus turns his anger on Adriana and she insists that he be restrained. Several men lay hold of Antipholus, who struggles with them. Adriana wants him taken to her house, but the officer insists that Antipholus is his prisoner until the debt is paid. She agrees to pay it, and Antipholus and Dromio are taken off by Pinch and his assistants.
Left to talk to the officer, Adriana learns that Antipholus had been arrested for the debt he owed Angelo for the chain. The courtesan informs her that Antipholus has both a chain and her ring, so Adriana decides to go see Angelo to sort things out. But then Antipholus and Dromio of Syracuse enter "with rapiers drawn" presumably they're afraid of anything they might encounter. Adriana thinks that Antipholus-E. and Dromio-E. have escaped, and the officer urges them to flee. Antipholus-S. is pleased to "see these witches are afraid of swords," and he tells Dromio to get ready to leave Ephesus.