Murder of King Duncan: The play opens with Macbeth's encounter with the three witches, who prophesy that he will become king. This ignites his ambition, but he is initially hesitant about committing regicide. However, with Lady Macbeth's persuasion and taunts about his manhood, Macbeth succumbs to his ambition and kills King Duncan. Almost immediately after the act, guilt begins to gnaw at him, and he becomes tormented by his actions.