Bosola enters in the dark with a lantern, saying that he has heard a woman shrieking from what seemed like the Duchess’s room. He notes that confining all of the courtiers to their separate rooms was most likely a strategy to stop them from figuring out what’s going on, and he decides to spy to get more information to report.
Bosola has apparently heard the pained shouts of the Duchess in labor, and he recognizes Antonio’s technique of confining the servants and courtiers to preserve the Duchess’s privacy.
Just then, Antonio enters with a candle and a sword drawn. Having heard a noise, he asks “who’s there?” Bosola responds that Antonio doesn’t need to be afraid, and he reveals himself. In an aside, Antonio calls Bosola a mole undermining him. He then asks if Bosola has heard a noise, and Bosola pretends that he did not hear one. Antonio claims that he has been calculating the loss from the robbery, but he puns on what he has really been doing: casting the horoscope of his newborn son.
Antonio’s “who’s there?” echoes the opening line of Shakespeare’s Hamlet. The drawn sword indicates the high stakes of the situation, and the confusion in the darkness also foreshadows the final confrontation between Antonio and Bosola. Like the Duchess, Antonio believes himself to be one step ahead of Bosola, so he is comfortable punning about his child.
Bosola asks if the loss was significant, but Antonio responds that it’s none of his business and questions why he’s out of his room when all men were ordered to their private lodgings. Bosola claims that he is out because he was praying. Antonio then questions whether the apricots Bosola gave the Duchess earlier in the day were poisoned. Bosola denies the accusation of poisoning, but Antonio says that some jewels were stolen and that Bosola is the number one suspect. The two men curse each other, but as they argue Antonio’s nose starts bleeding. In an aside, he notes that superstitious people would think that was a bad omen, but he calls it mere chance that his handkerchief is now “drowned in blood.” Antonio tells Bosola that he is forbidden to even go near the Duchess until Bosola is able to clear his name, and then Antonio exits.
Bosola uses religion as a pretense for being out of his room, but Antonio doesn’t buy it. He accuses Bosola of poisoning and robbing the Duchess, in part to cast suspicion off of himself. In a strange moment, Antonio gets a nosebleed; he knows that superstitious people would identify this as a bad omen, especially given that the blood is on his handkerchief, which would probably be embroidered with his initials. That Antonio is “drowned in blood” foreshadows the copious amounts blood that will be spilled before the play’s end.
Bosola then notices that Antonio dropped a piece of paper, on which he finds written the nativity horoscope that Antonio had just calculated. Bosola realizes he has the information he needs—he knows why the men have all been sent to their rooms. He suspects that he will be formally accused of poisoning the Duchess, but says he’ll laugh at the charge. He remembers that Castruccio is heading to Rome the next day and he decides to have Castruccio carry the horoscope in a letter to Ferdinand and the Cardinal.
Though he didn’t catch the horoscope pun when Antonio made it, Bosola discovers the paper containing the horoscope itself. He doesn’t piece together that Antonio is the father of the child, but he now has concrete evidence of the Duchess’s decision to disobey her brothers’ orders. At this point he does not show hesitation about fulfilling his duty as a spy and passing on the information.