Act Four opens with Lavinia chasing Lucius' son. The child is horrified by Lavinia's appearance, and must be calmed by Titus and Marcus. As they try to find Lavinia's reason for chasing the boy, she gestures to young Lucius' book, Ovid's Metamorphosis, and manages to turn the leaves to the story of the rape of Philomel. Titus thus gathers that she was raped. Marcus grabs a tree branch, and by placing one end of the branch between his teeth and guiding it on the sand with his arms shows how she might write the names of her assailants. She does so, informing the men that it was Chiron and Demetrius who raped her. Marcus and Titus both swear revenge, and Titus hatches a plot to send presents to the rapists before seeking revenge outright.
Per Titus' orders, young Lucius delivers Chiron and Demetrius the best weapons from Titus' armory with verses of Horace wrapped around them. Aaron enters to see the delivery, and immediately realizes that Titus has found out the facts of the crime. Meanwhile, we discover that Tamora is in labor. The nurse enters with the child, revealing that it is a black baby, and thus obviously Aaron's. The nurse then brings the child to Aaron and orders him to kill it. Demetrius and Chiron are appalled that Aaron and their mother have conceived a black child, and they both try to kill it themselves. Aaron, however, rescues the baby, swearing that he will protect his newborn son with his life, all while making fun of those with white skin.
When Chiron and Demetrius realize that Aaron is not going to kill his son, they decide to keep the birth a secret. Aaron kills the nurse so that she won't tell anyone about the child's existence, and instructs Chiron and Demetrius to buy the newborn child of a white countryman he knows in order to fool the emperor into believing his son to be white. He also tells them to send the midwife to him so that he can kill her too, thus eliminating everyone who knows about the birth, save for Tamora and her sons. Aaron leaves to join the Goths outside Rome's walls, planning to find a home for his child.
In the meantime, Titus' plot for revenge unfolds. Although his family and friends believe him to be mad, he convinces them to shoot arrows with letters wrapped around them into the Roman court. The letters advertise the injustices being perpetrated by the Roman government, and declare that since they can't find justice in Rome, they will seek out the justice of the gods. While shooting the arrows Titus comes across a pigeon-keeping Clown, whom he hires to deliver a personal message to Saturninus.
In the court, meanwhile, Saturninus is furious that Titus has been calling him unjust. Tamora calms him, silently plotting to deal with Titus herself. The Clown enters and delivers his message: yet another accusation of injustice. After reading the message, Saturninus orders the Clown hanged. Just then Aemilius arrives with news that Lucius has raised an army of Goths to march against Rome and depose Saturninus. The emperor turns pale upon hearing this, and swears that all is lost because the people of Rome love Lucius more than they love him. Tamora tries to snap her husband out of his self-pity with a rousing speech, and declares that she will have to use "all her art" to solve the Titus problem in an expedient manner.
The question of Lavinia's agency becomes even more complicated in Act Four. Despite the fact that Marcus knows she was raped and actually compared her to Philomel when he first found her, Lavinia is forced to prod her male protectors into action by getting them to read the story of the rape of Philomel in a volume of Ovid's Metamorphosis. (Her own metamorphosis is underscored by the fact that the young Lucius runs from her and treats the previously desirable woman like a monster.) Marcus' idea to use the tree branch as a writing instrument is another example of Lavinia's compromised agency: she is able to overcome her infirmity and name her rapists, but only by doing the bidding of her patriarchs. Thus Lavinia is both a catalyst for revenge and a submissive instrument, simultaneously active and passive. With Lavinia's insistence, the Andronici finally cease wallowing in self-pity, and move to take action.
Those who plotted and executed her rape, meanwhile, must deal with the problematic byproduct of another forbidden tryst: the child borne to Tamora and Aaron. The passage in which Aaron refuses to kill his child and expresses his belief in the superiority of black skin is one of Shakespeare's most remarkable: "What, what, ye sanguine, shallow-hearted boys! / Ye white-limed walls! ye alehouse painted signs! / Coal-black is better than another hue / In that it scorns to bear another hue; / For all the water in the ocean / Can never turn the swan's black legs to white, / Although she lave them hourly in the flood." Aaron deftly constructs a counter-narrative to Chiron, Demetrius, Tamora and the Nurse's hatred of the color black. He argues, in effect - hundreds of years before the Black Power movement of the 1970s - that black is beautiful, and he does so with more eloquence and wit than any of the other characters can muster in their claims to white superiority.
With the coming of his child, Aaron evolves from a clever, cruel trickster to a true sixteenth century anomaly: a (somewhat) sympathetic black man. Indeed, his pride in his color and his refusal to genuflect before white authority make Aaron more attractive in many ways than Othello. Aaron offers furious and scathing speeches during a manifestly racist time - the Elizabethan era - when the equation of black with evil and white with virtue was simply common sense.
As Titus' revenge proceeds apace, it is important to consider traditional Elizabethan conceptions of madness. The Elizabethans did not universally ostracize the insane. Some forms of madness, indeed, were to a degree socially acceptable - and one of these "acceptable" forms was madness stemming from an intense desire for revenge. The work that likely inspired Titus, The Spanish Tragedy, tells the story of another mad father, Hieronomo, whose thirst for retribution drives him mad. The subtitle on the play's title page in its original printing read: "Hieronomo is mad again." This and many other similar examples suggest that for the Elizabethans, madness and the desire for revenge were inseparable. The difficulty of seeking out justice in an unjust world made one mad - it was as simple as that.
Yet madness brought on by the need for revenge is not the same as full-blown insanity. With revenge-madness comes a certain clarity, a degree of subtlety. Think of Hamlet: for centuries, audiences and critics have wondered, "Is Hamlet really crazy, or is he just faking it?" The truth is, he is neither, and he is both. Revenge-madness, for the Elizabethans, did not always compromise the madman's sense of reality; he was still able to devise intricate plans for retribution. Titus, like Hamlet, is ambiguously insane. When characters in the play describe him as "mad", they are referring to the fact that he is justice-starved, not incapacitated. Even in his madness he is quite lucid - single-minded and absurd, yes, but wholly driven to consummate his vengeance as soon as the opportunity arises.