The porter says that he was up late carousing and rambles on humorously about the effects of alcohol, which he says provokes red noses, sleepiness, and urination. Being "effeminate" didn't mean you were like a woman—it meant you were too into women. Suspicion has now fallen on the two princes, Malcolm and Donalbain, because they have fled the scene.
In between all these antics, Romeo manages to take the Nurse aside and tell her that Juliet should find an excuse to come to Friar Laurence's church—where she will be married.
Lady Macbeth suddenly faints, and both Macduff and Banquo call for someone to attend to her. Macbeth and Lennox rush in to look, while Lady Macbeth appears and expresses her horror that such a deed could be done under her roof. His good-natured joking with Macduff breaks up the mounting tension of the play and also comments obliquely on its themes.
General chaos ensues as the other nobles and their servants come streaming in. He springs into action with a clear eye toward his purpose, seizing control of the nobles and becoming King of Scotland.
Malcolm declares that he will go south to England, and Donalbain will hasten to Ireland.