At Macbeth's new palace in Forres, Banquo, alone on stage, delivers a soliloquy: he's totally suspicious of Macbeth. But he does take the time to note that his part of the prophecy, regarding his royal seed, will also probably come true.
Macbeth comes along, and Lady Macbeth tells him to look more chipper and not dwell on dark thoughts, as "what's done is done."
With Banquo dead and Fleance on the run, the murderers head off to the dinner party to report the half of the job they've done.
Meanwhile, Macbeth is discoursing with the ghost that only he sees, and then it disappears. He swears to Lady Macbeth that the ghost was there, and then laments that it used to be that when you dashed a man's brains out he would die.
The witches again meet at an open place, this time with Hecate, the goddess of witches, who looks pretty angry.
Malcolm and Macduff are doing a pretty good job of convincing the oh-so gracious and "pious" King Edward of England, along with some English noblemen, to help them in the fight against Macbeth, the tyrant.