Banquo, Fleance, and Macbeth stop to speak about the three witches--Banquo mentioning strange dreams he has had of them whilst Macbeth explains he hadn't thought of them since their last encounter
When Banquo and Fleance leave, Macbeth has a vision of a dagger pointing him towards Duncan.
After killing Duncan, Macbeth encounters Lady Macbeth and expresses his guilt over his crime; hands still holding the bloodied knife as he stresses over his inability to say 'amen'.
Lady Macbeth gets angry over the fact that Macbeth had forgotten to leave the daggers with the chamberlains, going to do the task herself when Macbeth refuses to return to the murder scene.
Macduff discovers the King's corpse, quickly informing Lennox and Macbeth.
Upon seeing the body, Duncan's sons along with Malcolm and Donalbain decide that, in order to protect themselves from the murderer, they must flee. Duncan's sons decide to run from the court, Malcolm decides to go south to England, & Donalbain flees to Ireland.