At first Brutus' army has the upperhand over Octavius'. However, Brutus' soldiers get overconfident and direct their focuses on looting the town rather than finishing off their enemy. Meanwhile Cassius' army is losing to Antony's, causing Cassius to give up hope and ask his servant to kill him, even though the situation wasn't as dire as it seemed. When Brutus sees Cassius' dead body, he feels their plight is hopeless. Having previously agreed with Cassius that they'd take their own lives before being taken prisoner, Brutus runs onto his sword, held by Strato, ending his life and the war. Octavius and Antony are the winners and now share the power (along with Lepidus) in Rome.
The leaders of the two opposing sides meet to talk on the plains of Philippi. Their brief discussion only fuels their animosity and the two sides retreat to prepare for war. Brutus engages Octavius’ army while Cassius engages Antony’s side of the army. Brutus is victorious over Octavius, but Cassius suffers defeat against Antony. Cassius is worried and believes his friend has also been defeated by the opposition. He sees approaching soldiers and mistakenly thinks they are Antony’s men while in reality they were Brutus’ men on their way to deliver the good news. Due to the grief of supposedly losing his friend, and the fear of being captured, Cassius asks Pindarus to help him end his life. Pindarus holds Cassius' sword, and he runs on it. Brutus is saddened by the turn of events, but he returns for the second battle. The results are devastating for Brutus’ side and with the help of Strato, he runs on his sword. In the end, Octavius and Antony triumph over Brutus and Cassius.
Cassius stands on a hill and watches. It seems that the battle is slipping from Brutus, but nothing is certain. As for Cassius' army, it is not doing well. In fact, Pindarus comes to Cassius and says that he should flee, as Antony's men have taken Cassius's camp.
Cassius sends Titinius to find out what is happening. As Pindarus is watching, it seems that Titinius is captured. This grieves Cassius and he asks Pindarus to kill him. Cassius, therefore, dies. Cassius miscalculates everything. Titinius is not dead, and Brutus's army does not fair as badly as he thought. Brutus's army actually defeated Octavius's army.
Titinius sees what has happened and he takes his own life. When Brutus finds out what has happened, he cries out:
O Julius Caesar, thou art mighty yet: even in death, Caesar is reaping revenge; he seems to turn events against his murderers from beyond the grave.
Brutus is now left alone to fight again, which he does.