"O, full of scorpions is my mind, dear wife! Thou know'st that Banquo and his Fleance lives." (3.2.41-2)
"We have lost the best half of our affair." (3.3.31-2)
Banquo begins to have ambitious thoughts about his own son one day becoming king. In order to stop this Macbeth hires men to kill Banquo and his son in order to insure that he will stay king.
"Avaunt, and quit my sight! Let the earth hide thee. Thy bones are marrowless; thy blood is cold" (3.4.113-4)
Lady Macbeth calls for her husband, and Macbeth tells her of the deed he has planned without her. He says that he cannot be fully content with his kingdom if he does not finish this deed. He also urges lady Macbeth to be cordial to Banquo.
The hired murderers ambush Banquo and his son in the night, however in the middle of the skirmish their torch goes out, allowing Fleance to escape into the night while Banquo is slaughtered.
During a grand feast, Macbeth is notified of banquos death and Fleance's escape. He seems to be plauged by guilt as his mind conjures the spector of banquo sitting in the head chair. Macbeth speaks to the ghosts and the guests are shooed away by Lady Macbeth in an effort to preserve Macbeths Manhood.
Hecate scolds the witches for meddling in mortal affairs without consolting her, and says that she will supervise this mischief
I, the mistress of charms, / The close contriver of all harms, / Was never called to bear my part / or show the glory of our art? (3.5.6-9)
Lennox is informed of Macbeth's horrid actions and hopes fervently that Malcolm and Macduff can save the kingdom from the tyrant Macbeth.
"His message ere he come, that a swift blessing / May soon return to this our suffering country / Under a hand accursed!" (3.6.53-5)