After realising Banquo's sons will be kings, Macbeth orders Banquo to be killed. Banquo is killed, however his son, Fleance survives and flees.
Macbeth, whilst dining with friends, hallucinates and sees the ghost of Banquo sitting in a chair. The ghost chases him, then disappears, leaving the attendants to fear for his health.
Macbeth revisits the witches, who inform him that he should be afraid when he is attacked by Birnam wood. He is also told that he cannot be harmed, and therefore killed, by any person "of woman born", which leads him to believe he is invincible.
Macduff, who's family has just been killed by Macbeth, pleads with Malcolm to lead an army against Macbeth. He agrees, and they plan to hide their troops by charging at the castle whilst brandishing branches, therefore Birnam wood is attacking.
Lady Macbeth, stricken with guilt, sleepwalks to her doctor, tells them everything, and then kills herself. Macbeth hers the news as he is going into battle, and mourns.
Macbeth and Macduff fight. Macbeth isn't afraid until Macduff reveals he is born of a C-section, which means he is not of woman born. Macbeth gives up and is killed. Malcolm, by bloodline of Duncan, becomes king and declares peace.