Barabas enters reading a letter which informs him of Abigail's conversion. In it, his daughter begs him to repent. Barabas is enraged and condemns Abigail, saying that because she thinks differently than Barabas does about morality she cannot really love him. When Ithamore appears, Barabas offers him warm words of greeting saying, "I now have no hope but even in thee." The slave informs his master that Abigail met with the priest. Barabas makes another biblical allusion to Cain being cursed by his father Adam and calls Abigail "false." Ithamore cajoles Barabas's with gentle flattery, saying that he will do anything for his "sweet sake." Barabas promises to make Ithamore his heir and bequeaths half his wealth to him straight away, but Barabas does not actually give the slave the keys to his money. Barabas instructs Ithamore to bring him a pot of rice from the fire. The slave does so, and Barabas informs him of his intention to kill Abigail by poisoning the rice. Barabas explains that the poison he is using is a powder from Ancona, which takes effect forty hours after it is ingested. Ithamore must carry the pot to the convent and leave it there as alms, taking care that no one sees him. Barabas curses the pot before Ithamore leaves, comparing it to the "draught great Alexander drunk" and "Borgia's wine, / Whereof his sire, the Pope, was poisoned." Ominously, Barabas vows to pay Ithamore "with a vengeance" for his faithful service.
Ferneze meets with the Bashaw (a Turkish emissary) who has come to collect the agreed-upon tribute. The governor states that he will not pay what he has promised, and so the Bashaw states that Calymath will attack Malta. Ferneze instructs his officers to prepare the fortress for battle, declaring "nought is to be looked for now than wars, / And nought to us more welcome is than wars."
Two friars, Jacomo the Dominican and Bernardine, discuss the poisoning of the convent. Although both are panicked, they talk about visiting dying nuns in a way that suggests they will be doing more than hearing the women's last confessions. Jacomo leaves, and Abigail arrives looking for him. Barabas's daughter agrees to confess to Bernardine because she is about to die. Abigail tells him all about her father's role in Mathias's and Lodowick's deaths and gives him a paper describing in it more detail. Although Bernardine is disgusted, he recognizes he cannot make public what he has learned in a confession. Abigail dies beseeching the priest to try and convert her father, saying, "witness that I die a Christian." Bernardine only regrets that she has died a virgin. Jacomo reappears and informs the priest that all the nuns are dead. Bernardine tells Jacomo that they must denounce "the Jew" for the terrible thing he has done. The Dominican asks whether Barabas has "crucified a child" to which Bernardine replies that it is a worse crime but that he cannot reveal the details of it.
Vengeance and betrayal are in the foreground of Act III, scene iv, but still remain secondary to the theme of money. Barabas vows revenge against his daughter and even threatens Ithamore at the end of the scene. As shrewd as ever, the protagonist promises to make Ithamore his heir but does not give him the keys to his money chests. Marlowe makes it clear that even in his despair at Abigail's conversion, Barabas has enough presence of mind to jealously guard his wealth. Undeniably, money is the protagonist's primary concern. Ithamore's dedication to his master increases as he realizes that he will profit by faithful service, and the slave becomes positively ingratiating in his bid to garner Barabas's admiration. For example, before Barabas poisons the rice, Ithamore says, "Pray do, and let me help you master. Pray let me taste first." This scene reinforces how enslaved Barabas and Ithamore are to the idea of money and how this affects their personal motivations.
The playwright returns to his motif of nothing in Act III, scene v. The governor states that there is "nought" to expect but "war," reinforcing a sense of lack that seems to hang over the text. While all of the characters scrabble for gold, not one seems the least bit content. Ferneze decides to fight Turkey because he does not want to lose his money—or more accurately, the riches he coerced from the Maltese Jews—in tribute to Calymath. Thus, the governor has a great deal more than nothing. Although the governor's speech is distractingly heroic as he entreats his "men of Malta" to "courageously encounter" the Ottoman army, the comment which most aptly sums up the situation is Ferneze's request that his officers "profitably take up arms" in battle.
In Act III, scene vi, Marlowe makes several jibes against the celibacy of priests. Bernardine rues the fact that Abigail died a virgin, and both friars are on intimate terms with the nuns—for example, Jacomo leaves to visit "fair Maria" in her lodgings. Despite this vice, Bernardine is self-righteously indignant when he hears of Barabas's plot to kill Mathias and Lodowick, describing it as a "monstrous villainy." Jacomo's question as to whether the protagonist killed a child could well have been taken seriously by Elizabethan audiences, who believed in the blood libel perpetrated by Christians against Jews in Europe. Since the Medieval period, stories abounded about Jews poisoning wells at night (such as Barabas admits to in Act II, scene iii) and murdering Christian children. But Bernardine's response to Jacomo is telling: Barabas is worse than other Jews, since the crime he committed is apparently more heinous than butchering a child. It is hard to say whether Marlowe is sending up common preconceptions about Jews, or if he is playing on the fear their demonized role within society would have aroused in contemporary audiences. We might recall Barabass' statement in Act I, scene ii that he should not be held accountable for the "transgression" of his "tribe." Once again, we see that Barabas's criminal nature is being associated with his Jewish identity.