Detailed Summary of Macbeth, Act 1, Scene 1
Thunder and lightning. Enter three Witches:
In the play as a whole, people are tossed about by forces that they cannot control, and so it is in the opening scene. The witches, blown by the storms of nature and war, swirl in, then out. As soon as we see them, they are on their way out again, and the first one is asking, When shall we three meet again? / In thunder, lightning, or in rain?" (1.1.1-2).
They will meet when "the battle's lost and won" (1.1.4). Note the "and." It's not when the battle is lost or won. If someone wins, someone also loses; it doesn't really matter to the witches, who don't take sides with people, only against them.
The first witch asks where they will meet, and the other two tell her that it will be upon the "heath," a barren, windswept place, in order to meet Macbeth. Then they're off, called by their familiar spirits, one of which inhabits a grey cat, and another of which lives in a toad.
As they leave, they chant a witchy chant: "Fair is foul, and foul is fair: / Hover through the fog and filthy air" (1.1.11-12). As creatures of the night and the devil, they like whatever is "foul" and hate the "fair." So they will "hover" in the fog, and in the dust and dirt of battle, waiting for the chance to do evil.