The play opens on the streets of Rome where common citizens celebrate Julius Caesar's triumphant return, prompting tribunes Flavius and Marullus to angrily disperse the crowd for their fickle disloyalty to the memory of Pompey. During the festival of Lupercal, a soothsayer warns Caesar to beware the Ides of March, an omen he dismisses as mere foolishness. Meanwhile, the cunning Cassius works carefully to manipulate the noble Marcus Brutus, playing upon Brutus's deep love for Rome to convince him that Caesar's rising ambition poses a severe threat to republican liberty. Cassius gathers a circle of disgruntled senators, including Casca, Cinna, and Metellus Cimber, who resolve that Caesar must be eliminated before he can be crowned king.
As the fateful night before the Ides of March unfolds, Brutus wrestles intensely with his conscience in his orchard, ultimately concluding that Caesar must be killed not out of personal malice, but as a preventative measure for the general good of Rome. Portia, Brutus's devoted wife, begs him to share the source of his profound distress, proving her constancy by inflicting a deliberate wound upon her thigh. Despite troubling omens, violent tempests, and Calphurnia's desperate pleas for her husband to stay home after dreaming of his statue spouting pure blood, the persuasive Decius convinces Caesar to venture forth to the Senate-house by flattering his pride and reinterpreting the dream as a sign of reviving fortune.
At the Capitol, the conspirators press close around Caesar under the guise of presenting petitions, with Metellus Cimber pleading for his banished brother's repeal. When Caesar responds with unyielding arrogance, comparing his steadfastness to the northern star, Casca strikes the first blow from behind, quickly followed by the rest of the conspirators. As Marcus Brutus delivers the final stab, Caesar utters his famous final words before collapsing at the base of Pompey's statue, and the assassins cry out for liberty and freedom while bathing their hands in his blood.
Mark Antony, having fled in initial terror, sends a servant to negotiate safe passage so he can speak with the conspirators. Though Cassius remains deeply suspicious, Brutus grants Antony permission to speak at Caesar's funeral, provided he does so after Brutus addresses the public and only with their explicit consent. In the Forum, Brutus delivers a rational defense of the assassination, persuading the crowd that Caesar's ambition necessitated his death for the preservation of their freedom.
Antony follows with a masterfully subversive funeral oration that turns the tide completely against the conspirators. By repeatedly calling the assassins honorable men while deliberately highlighting Caesar's humility, his grief for the poor, his refusal of the crown, and the generous provisions left to the citizens in his private will, Antony inflames the mob into a fury of grief and vengeance. The enraged populace riots through the streets, driving the conspirators from Rome and mistakenly tearing apart Cinna the poet merely because he shares a name with one of the murderers.
Abroad, Antony joins forces with Octavius Caesar and Lepidus to form a new triumvirate, ruthlessly executing political rivals and preparing their military forces for war. Meanwhile, a bitter rift erupts between Brutus and Cassius at their military camp near Sardis over accusations of corruption and withheld funds, though the two soon reconcile after grieving deeply over the tragic suicide of Portia, who swallowed fire in her husband's absence.
As the opposing armies converge on the plains of Philippi, both sides trade insults before engaging in a fateful battle. Misunderstandings and the fog of war lead to disaster when Cassius, falsely believing his close friend Titinius has been captured by the enemy, despairingly commands his captive servant Pindarus to assist him in ending his own life with the very sword that killed Caesar. Upon discovering the grim scene, a heartbroken Titinius places a victory garland on his fallen general's brow and takes his own life as well.
Facing overwhelming defeat in the second confrontation, and visited twice by the ghost of Caesar warning of his impending doom, Brutus chooses a soldier's honorable end rather than face the humiliation of being led in chains through Rome. He runs upon his own sword held by the loyal Strato, leaving the victorious Antony to pronounce him the noblest Roman of them all for acting out of genuine concern for the common good while the other conspirators were driven solely by envy.
