In act 1, scene 2, Cassius tries to sway Brutus to rise against Caesar for Rome's well being. Brutus likes Caesar, but does not believe he will be a good king for Rome. When trumpets are sounded Brutus says, "I do fear the people choose Caesar for their king" (I:ii:ln 78-79). This is the beginning of many major events and Brutus joining the conspiracy.
Act IV: Sc 3
In act 2, scene 1, Brutus is visited by Cassius and five other conspirators covered in cloaks at night. Cassius is the only one not cloaked, and he introduces each of the conspirators to Brutus. Brutus then decides to join their plot, and welcomes each of them saying, "give me your hands all over, one by one" (II:i:ln 112). The group of conspirators then plot how they will go about killing Caesar for the good of Rome.
Act V: Sc 5
In act 3, scene 1, Caesar is killed by Cassuis, Brutus, and the other conspirators. Caesar's final words are, Et tu Brutè? Then fall Caesar" (III:i:ln 79). Caesar's final words show how much Caesar cared for Brutus. This leads to Antony claiming that Caesar did not die from stab wounds, but from the broken heart of his friend Brutus killing him, and then starting a war.
THEME Act 5: Sc 5
In act 4, scene 3, Cassius and Brutus get into a heated argument. Once the two are finished arguing, Cassius blames his short temper on his mother, saying, "Have not you love enough to bear with me when that rash rash humor which my mother gave me makes me forgetful? (IV:iii:ln 117-119). Then the two started to plan for war. This is important because it sets up the future events of the war, and shows how the weight of their actions have affected their relationship.
In act 5, scene 5, Brutus took his own life to end the conflict. With his last words, Brutus blamed Caesar for all the bad events that have occurred, saying, "Caesar, now be still; I killed not thee with half so good a will" (V:v:ln 50-51). With his death, Brutus finally brought the end to the tragic events that occurred from Caesar being killed. Brutus also died on his own terms, and in doing so had the noblest death.
I believe the theme of this story can be found in act 5, scene 5, when Antony says, "This was the noblest Roman of them all. All the conspirators save only he did that they did in envy of great Caesar," (V:v:ln 68-70), in front of Brutus's body. The theme shown here is that the noblest way to live, and die, is by doing what you believe is correct. Brutus, in death, is honored even by his adversaries because of the way he commits his actions. In conclusion the most fulfilling way to live your life is by staying true to your morals and beliefs.