Brutus is with his army in the field. He asks Lucilius how his meeting with Cassius went, and is dismayed to learn that Cassius seemed to be acting coldly. Cassius arrives, and Brutus asks to speak privately. Cassius complains about Brutus disciplining one of Cassius’ subordinates, and Brutus in turn accuses Cassius of taking bribes. Brutus argues that they must wage war honorably, or the killing of Caesar was hypocritical. Cassius contends that a practical approach is the only way to win the war. Brutus becomes angry with Cassius’ boasting and the argument becomes heated, until finally the two men make up.
An old poet barges into the camp, and tries to convince the two men to stop fighting with a simplistic poem before he is thrown out. Brutus and Cassius have wine together in Brutus’ tent, and Brutus tells Cassius that Portia killed herself by swallowing hot coals. Titinius and Messala enter with news that Cicero has been killed on Antony’s orders, along with many other senators. The men discuss whether and how to meet Antony and Octavius at Philippi, and eventually yield to Brutus’ plan. Brutus and Cassius swear friendship, and the others leave Brutus alone in his tent. He asks for Lucius to play music, invites his guards to sleep in the tent while he keeps watch, and tenderly watches Lucius as the boy falls asleep. The ghost of Caesar appears, calling himself Brutus’ evil spirit. Brutus is startled and wakes the others, who noticed nothing. Brutus gives orders to Varro and Claudius to tell Cassius begin the march first.