In Act 3, Scene 2, Macbeth is talking to Lady Macbeth just before the evening's big formal dinner. Macbeth is determined to free himself of all enemies and especially Banquo and Fleance. Banquo is more than suspicious of Macbeth, and the witches said that Banquo's children would live to be kings, generation after generation. He wants Banquo and Fleance dead this very night.
The mood created by the following exchange is one of darkness and danger, anger, fear, determination and death:
O, full of scorpions is my mind, dear wife!
Thou know'st that Banquo and his Fleance lives.
But in them nature's copy's not eterne.
There's comfort yet; they are assailable.
Then be thou jocund. Ere the bat hath flown
His cloister'd flight; ere to black Hecate's summons
The shard-borne beetle with his drowsy hums
Hath rung night's yawning peal, there shall be done
A deed of dreadful note.
What's to be done?
Be innocent of the knowledge, dearest chuck,
Till thou applaud the deed. Come, seeling night,
Scarf up the tender eye of pitiful day,
And with thy bloody and invisible hand
Cancel and tear to pieces that great bond
Which keeps me pale! Light thickens, and the crow
Makes wing to the rooky wood:
Good things of day begin to droop and drowse,
Whiles night's black agents to their preys do rouse.
Thou marvell'st at my words, but hold thee still:
Things bad begun make strong themselves by ill.
So, prithee, go with me.