Young Lucius arrives at the door of the emperor's palace with gifts. Titus has sent Chiron and Demetrius the best weapons from his arsenal, along with a note (written in Latin) that says something like: "The man who is pure of life and free from crime needs not the arrows or the bows of the Moor." This, by the way, is a quote from Horace's Odes (I.xxii, 1-2).
Chiron is all "Hey, I know that line. I read Horace in school."
Aaron is the only one who gets Titus's little joke, and he says as much.
A nurse enters the room with some news: Tamora has just given birth. (Surprise!)
The nurse declares that everyone's in trouble now because the little bundle of joy, unlike its mother and her husband the emperor, is very dark-skinned.
Aaron is the only person happy about this news. The nurse calls the baby a "devil" that's "as loathsome as a toad" and says that Tamora wants Aaron to "christen it" with a "dagger's point."
Aaron screams "Zounds, ye whore, is black so base a hue?" and proceeds to make fun of the nurse's ruddy complexion.
Chiron says that Aaron has "undone" his mother, and Aaron promptly retorts that, no, he's actually "done" Chiron's mother, which is why she just gave birth to a baby with skin as dark as his.
Demetrius threatens to stab the little "tadpole," and Aaron, who has suddenly become a protective father, threatens to stab someone in the guts if they mess with his kid.
Demetrius, Chiron, and the nurse worry that Tamora is going to be in serious trouble when the emperor sees the baby.
After hearing that the nurse and a midwife named Cornelia are the only people who know about the baby (besides Tamora and present company), Aaron kills the nurse and coldly yells out "Weeke! Weeke! So cries a pig prepared to the spit."
Aaron orders Chiron and Demetrius to take a bunch of money to a couple that lives in the country. They've just given birth to a baby with a light complexion. Aaron wants to buy it and pass it off as the child of Saturninus and Tamora. He reasons that the couple will agree, because who wouldn't want their kid to be raised as an heir to the Roman empery?
Aaron takes his baby to a cave, where he plans to feed the child goat's milk and berries and raise it to be a great warrior.