In Antium, Coriolanus asks for admission to the house of Tullus Aufidius. Aufidius' servants refuse to allow him in, as he is dressed in humble clothing, but one of them fetches his master. The Volscian general does not recognize Coriolanus either, so the Roman identifies himself and says that he has come to offer his friendship to Aufidius and support to the Volscian cause, or to be killed--it matters little to him. Aufidius, overcome with emotion, embraces him as a friend and welcomes him in, promising him the opportunity to exact revenge on the Romans for his banishment. The two generals dine together, and one of the servants brings word to his fellows that there will soon be war with Rome.
Back in Rome all is quiet, and Brutus and Sicinius congratulate each other on the ease with which they disposed of the troublesome Coriolanus. There has been no news from the exile for some time, and they tell Menenius that the city is better off without him. Just then, a messenger brings word that Aufidius and the Volscians are preparing to make war on Rome again. Brutus refuses to believe the news, but a second messenger brings even worse news--not only is the army indeed marching on Rome, but it is led by Coriolanus himself. Menenius is joined by Cominius, and the two friends tell the tribunes that this catastrophe is their fault--that their folly will bring down destruction on Rome. Brutus and Sicinius protest, but now the plebeians come in, panicked by the tidings, and begin to say that they were wrong to banish Coriolanus. The two tribunes, fearing for their own position, depart for the Capitol.
Meanwhile, Aufidius is beginning to have second thoughts about his alliance with his former adversary, as his soldiers have become begun to show more devotion to Coriolanus than to him. He assumes that Rome will fall to her exiled general, and he begins to plot a way to dispose of Coriolanus once the city has been taken.
Coriolanus arrives on the borders of the city with his army, and Cominius goes out to plead with his old friend for mercy. Coriolanus turns him away, however, to the great despair of the inhabitants of Rome. Brutus and Sicinius plead with Menenius to make his own attempt, and the old patrician reluctantly agrees. However, as he departs, Cominius tells the tribunes that there is no hope-- Coriolanus is immovable.
For the moment, the two great adversaries stand united: The sight of Coriolanus has overwhelmed Aufidius' feelings of enmity and resentment--although these will return in double force later on. Early in the play, Coriolanus had remarked of Aufidius that "were I anything but what I am, / I would wish me only he (I.i.229-30)," and the Volscian general apparently feels the same way: "Know thou first," he tells his old enemy, "I loved the maid I married... But that I see you here, / Thou noble thing, more dances my rapt heart / Than when I first my wedded mistress saw / Bestride my threshold (IV.iv.117-22)." There is more than a hint of homoeroticism here, and it only increases when Aufidius describes to Coriolanus how he fought him in his dreams: "We have been down together in my sleep, / Unbuckling helms, fisting each other's throat." The muscular warrior culture, it seems, easily lapses into a kind of sadomasochistic sexual fantasy.
In their intemperate banishment of Coriolanus, the tribunes forfeited the audience's favor; now, in their preening self-satisfaction over "the present peace" that grips the city, they become absurd. "Do they not know the mistake they have made?" we wonder incredulously. Indeed, they realize it quickly enough, although their misplaced confidence is so great that they temporarily disbelieve the tidings of Coriolanus's approach. Menenius takes a kind of perverse delight in tormenting the unfortunate tribunes with their folly, though a fear for his city necessarily tempers this delight. Meanwhile, Brutus and Sicinius exhibit no real response to the news; they are not warriors, their political intrigues will be useless against a Volscian army. They can only express the wish that the news were untrue. Thus Brutus says, "Would half my wealth / Would buy this for a lie! (IV.vii.161-62)."