A knocking is heard on the castle gates, Lady Macbeth returns, but her husband is already regretting what he has done. The castle porter goes to open the door.
The porter imagines himself to be the porter of hell-gate, welcoming various types of sinner. He admits Macduff and Lenox and jokes with them about the effects of alcohol.
Macbeth enters and shows Macduff where Duncan is lodging. Lenox describes the strange unnatural events of the previous night.
Macduff enters, crying out in horror at his discovery of Duncan’s murder. As Lenox and Macbeth go to see the sight for themselves, Lady Macbeth enters.
Macbeth returns and expresses his shock. Duncan’s sons, Malcolm and Donalbain, are told of their father’s murder at the hands, it seems, of his bodyguards.
Macbeth explains why he killed the bodyguards. As he describes his vision of the murdered Duncan, his wife faints and is carried out. Duncan’s sons privately show their fears for their own safety.