The Fall of Macbeth
Now that Macbeth's king, he's absolutely paranoid about the witches' other prophecy - that Banquo's descendants will rule Scotland. So he hires murderers to kill Banquo and his son Fleance. They manage to kill Banquo but Fleance escapes, which terrifies Macbeth because the threat to his throne is still alive.
Things get properly weird when Banquo's ghost shows up at a royal feast. Only Macbeth can see it, and he completely loses it in front of all the Scottish nobles. Lady Macbeth tries to cover for him, but everyone's now suspicious of their king.
Desperate for answers, Macbeth visits the witches again. They give him new prophecies: beware of Macduff, no man "born of woman" can harm him, and he's safe until Birnam Wood comes to Dunsinane. Feeling invincible, Macbeth orders the brutal murder of Macduff's entire family when he learns Macduff has joined Malcolm's army in England.
The end comes quickly. Malcolm's army disguises itself with branches from Birnam Wood (so the forest literally moves to Dunsinane), and in the final battle, Macduff reveals he was born by caesarean section - technically not "born of woman." Macduff kills Macbeth, and Malcolm becomes the rightful king.
Key Point: The witches' prophecies all come true, but not in the way Macbeth expected - Shakespeare loves this kind of dramatic irony.