After defeating two separate armies, Macbeth and Banquo come across a trio of witches who prophesy Macbeth's rise to the throne and Banquo begetting a line of kings. Macbeth starts to believe the prophecy when a part of it comes true. Encouraged by Lady Macbeth's ambition, he kills King Duncan. William Shakespeare's harrowing tragedy, Macbeth, explores the curse of greed and the amoral power of unchecked ambition.