Brutus is awake late at night. He tries to justify killing Caesar, saying that although Caesar seems honorable now, there is too great a risk that he may be corrupted by power. Brutus reads one of the letters that was left for him. The letter accuses him of not taking action to prevent corruption in Rome.
When Cassius and the conspirators visit Brutus, he agrees to kill Caesar, but argues against swearing an oath because that the nobility of the group and the fact they have all discussed the act together means they should not need an oath to keep their resolution. Decius Brutus asks if they should kill anyone else besides Caesar, and Cassius suggests Mark Antony, but Brutus strongly opposes the idea on both moral and practical grounds, and the others follow his lead.
Eventually the conspirators decide to split up, and Decius Brutus volunteers to make sure Caesar makes it to the Capitol the next day. Brutus’ wife Portia comes in and demands to know what Brutus has been keeping from her. Brutus praises her but says he must wait a little longer to tell her. The sick Caius Ligarius enters, and when Brutus tells him of the plot against Caesar, he immediately agrees to join and resolves to be well again.