In ancient Rome, a mob of angry plebeians riot on the streets because (1) they are totally starving and (2) the patricians (a.k.a. the ruling class of powerful aristocrats) have been hoarding all the grain. Yep, Rome's experiencing a famine, and the plebeians blame all their problems on one patrician in particular: Caius Martius. (HUGELY IMPORTANT: This dude will later earn the nickname "Coriolanus", but for now, he's just plain "Caius Martius," aka Rome's resident war hero slash arrogant snob slash biggest hater of the lower classes.)
One of Martius' pals (a guy named Menenius) rolls up onto the scene and manages to sweet talk the mob into dropping their weapons. But then Martius shows up and immediately starts hurling insults at the crowd and egging them on. (Hmm. We probably would have taken a different approach. Guess that's why this play isn't named after us.)
Before this blood-thirsty mob has a chance to tear his limbs apart, Caius Martius is called off to fight in a war against the "Volsces who are planning an attack on Rome. Meanwhile, two newly elected Roman tribunes named Sicinius and Brutus complain that Martius needs to be taken down a notch. They plot to destroy him ... just as soon as Mr. Arrogant Grain Hoarder gets back from saving Rome, that is.
When Martius and his soldiers show up at the Volscian city of Corioles, Martius shows us why he's considered a war hero: he singlehandedly slaughters a bunch of guys in combat, which inspires his troops to waste the entire city. For his heroism, Martius gets a shiny new nickname: "Coriolanus." (As in, the guy who just crushed the city of Corioles.) He returns to Rome like a rock star and quickly decides to cash in on his popularity by running for the highest political office in Rome: consul
In order to win the election, Coriolanus has to act all humble and "beg" the plebeians for their votes, even though he totally hates them and can't stand acting like a phony politician. At first, the plebeians agree to give him their votes but then our scheming tribunes (remember Sicinius and Brutus?) convince the people to change their minds and take them back. When Coriolanus gets the bad news, he flips out, talks some serious trash about the plebs, and winds up inciting another riot.
Coriolanus' friends and his mom beg him to apologize. He tries, he really does, but he can't keep his big mouth shut and gets booted out of Rome. He naturally want to get his revenge on, so he joins up with his sworn enemy Tullus Aufidius and leads a Volscian army against his home town. Just before he and his new army are about to demolish Rome, his mom, wife, and kid show up and beg him to show some mercy. (Women, right??) Coriolanus tries to be all hard core, but he gives in at the last minute and arranges for a peace treaty.
Rome is safe, but Coriolanus has some explaining to do. He and his crew go back to the city of Corioles to face the Volscians, who aren't exactly happy that Coriolanus made peace with Rome. Plus, Tullus Aufidius is super jealous of Coriolanus' popularity with the Volscians. Aufidius schemes with a group of Conspirators to accuse Coriolanus of being a traitor. In public, they accuse him of treason and kill him. (Trial? What trial?) After the deed is done, the Volscians feel bad (sort of) and arrange an honorable burial for Coriolanus' body.