Cassius and Titinius enter, with Cassius carrying a battle flag.
Cassius tells Titinius that when his own flag-bearer started running away, Cassius killed him for his cowardice.
Titinius says that Brutus gave his orders too soon, giving Antony’s men an opportunity to surround them. Pindarus enters, urging Cassius to quickly retreat—Antony’s forces are overrunning them.
As Titinius rides off to scout out the situation further (he says he’ll be back faster than the speed of a thought), Cassius reflects that on this, his birthday, his life has run its full course.
Pindarus reports that Titinius has been taken captive by the enemy. Appealing to Pindarus’s personal loyalty to him, Cassius orders Pindarus to stab him to death. Pindarus does so, with the same sword Cassius used to stab Caesar. Then, in grief, he flees Rome forever.
Titinius and Messala enter. Messala tells Titinius that Octavius has been overthrown by Brutus, just as Cassius has been overthrown by Antony.
Then they discover Cassius’s body on the ground. Titinius grieves his friend’s death: “the sun of Rome is set” because Cassius didn’t trust that Titinius would be successful in his scouting errand. Messala shares his grief, lamenting that despair moves people to irreparable error.
Messala goes to give Brutus the sorrowful news while Titinius searches for Pindarus.
However, alone with Cassius’s body, Titinius lays his victory garland on Cassius’s brow and then kills himself with Cassius’s sword.
Brutus, Messala, and several others enter. When they discover both Cassius’s and Titinius’s slain bodies, Brutus laments that Caesar’s ghost “walks abroad and turns our swords; In our own proper entrails,” and that Rome will never produce an equal to Cassius.
Brutus sends Cassius’s body outside the camp for burial, saying that he’ll find time to mourn Cassius privately, and leads the others off for a second fight.