Without a doubt the main event is the killing of Duncan by Macbeth. That, of course, is central to the play. Before that occurs in scene 2, there is a brief conversation between Macbeth and Banquo in which Macbeth tells Banquo he'd like to talk to him sometime on a topic that has something to do with the three witches., and furthermore, what Macbeth has to say to Banquo could be good for Banquo's future. Banquo's reply is odd because he says he'll talk with Macbeth as long as doing so doesn't require him to be disloyal to the king or to do something that would go against his conscience. This suggests that Banquo might already suspect that Macbeth is up to something where Duncan is concerned. After Banquo leaves that scene, Macbeth sees the "air-drawn dagger". This lets us know that Macbeth's conscience is already bothering him. Was it something that Banquo said or does Macbeth, at this point in the play, still have a soul that is bothered by the thought of killing the king? Clearly though, Macbeth's ambition reigns over his conscience. Macbeth's actions after he kills Duncan in scene 2 suggest that he immediately regrets his actions, but he is still savvy enough in scene 3 to immediately kill the guards to prevent them from denying that they killed Duncan. Scene 3 starts with the comic relief scene in the play. The drunken porter is complaining that he has to get up to answer the knocking at the castle gate. Then he and Macduff have a humorous exchange about the effects of drinking too much alcohol. The funny scene is quickly exchanged in scene 3 when Macduff discovers Duncan's bloody body. Things are chaotic for the rest of the scene with Macbeth killing the guards, Lady Macbeth fainting, Duncan's sons - Malcolm and Donalbain - receiving the news of their father's murder. The two sons, at the end of scene 3, suggest that the murder was an inside job and that they'd better get out of the country for their own safety. For that reason, too, they split up with Malcolm headed to England and Donalbain headed to Ireland. The last scene of Act 2 is a short one in which an old man talks with Ross and reports that the night of Duncan's murder, other odd things were happening. Ross also reports of very unnatural events taking place that night including horses that turned cannibalistic. The purpose is to show what happens when God's plan is upset. (Shakespeare wrote Macbeth, in large part, to honor the new king of England, King James I who was from Scotland and who believed that God ordained who should be king so the killing of a king was, essentially, upsetting God's plan.) Also, in scene 4, we learn that the general assumption is that Malcolm and Donalbain fled the country because they were guilty of hiring the guards to kill Duncan.