Vindice (still in disguise) leads Lussurioso to the Duchess’s chamber. Lussurioso draws his sword, hoping to kill Spurio, but discovers that the Duchess is in bed with the Duke instead. The Duke frantically begs for his life, saying he has days’ worth of prayers to ensure he goes to heaven.
The Duke reacts cowardly to the intruder, whom he doesn’t initially realize is his own son. It’s telling that, when confronted with the end of his life, the Duke feels he ought to pray. The fact that he has days’ worth of prayers to make firstly suggests the sheer number of misdeeds he has committed through his life, and secondly that, like sex and justice, he sees the access to a good afterlife as essentially transactional—he believes he can exchange prayers for heaven.
The Duke realizes that Lussurioso is his assailant; the Duke’s guards seize Lussurioso. Some noblemen, Ambitioso, and Supervacuo enter. The Duke and the Duchess express their surprise that Lussurioso had come to assassinate his own father. Sensing it best that they get out of there, Vindice and Hippolito make a swift exit.
Lussurioso, of course, hasn’t come to kill his father, but rather to kill Spurio. The lack of bloodshed here heightens the audience’s anticipation for its later arrival.
Spurio enters with his servants. Lussurioso tries to tell the Duke about the Duchess’s affair with Spurio but is silenced and taken to prison. On his way out, Lussurioso pleads with Ambitioso and Supervacuo to secure his freedom, which they pretend to commit to.
The Duke demonstrates his power in administering justice. Ambitioso and Supervacuo live up to their names—they’re only interested in trying to find a route to power.
Ambitioso and Supervacuo speak to the Duke. Though their intention on the surface is to bring about Lussurioso’s release, they deliberately try to subconsciously influence the Duke to punish Lussurioso as harshly as possible, telling him that that’s what others would have done. The Duke instructs them to go and tell the judges, “He shall die.” As they leave, the Duke makes clear that he sees through Ambitioso and Supervacuo’s power-hungry scheming.
The play’s plot starts to complicate as vendettas between different characters become increasingly apparent. The Duke doesn’t really want to kill Lussurioso because he is his only true son and heir (Spurio is a bastard and the others are the Duchess’ children, not his). The Duke’s directive to tell the judges only that a nonspecific “he” be punished to death will result in the misunderstanding that leads to Junior Brother’s death.
With Ambitioso and Supervacuo gone, the Duke tells his noblemen that he will pardon Lussurioso. Left alone on stage, the Duke reasons that he ought to forgive those sins that are less grave than those he has committed himself throughout his life. He talks of his lustiness, and his punishment for those who don’t give in to his sexual demands: “Many a beauty have I turned to poison / In the denial, covetous of all.”
This is a rare insight into the psyche of the Duke, revealing a nihilistic admission of his evil acts. The exploitation of beauty—that is, acting on his lust—is more important to him than life itself. The mention of poison relates to Gloriana, Vindice’s deceased wife, but also implies that she isn’t the only one he has murdered for the same reasons. It also foreshadows his own death (and its method).