The king, Duncan listens to a report about a battle. He hears how Macbeth and Banquo, the Scottish generals, just defeated two armies. Duncan then announces that the thane of Cawdor should be executed and his title now given to Macbeth.
After the battle, Macbeth and Banquo meet the three witches and they start talking to Macbeth, calling him "the thane of Cawdor" (he still doesn't know that this is now true) and the future king of Scotland. The witches also tell Banquo his children will be future kings, then they vanish.
Duncan announces he is making his son, Malcom the heir to the throne.
Lady Macbeth receives and reads a letter, sent by her husband, about the witches prophecy. She immediately decides this must come true, even if Macbeth won't want to kill Duncan. Macbeth then tells her the king will be spending the night in their castle and she makes all the plans to kill him, telling Macbeth not to worry about it however seeing he is getting anxious.
After much consideration and persuasion from Lady Macbeth, Macbeth goes through with the plan and kills Duncan. Then Lady Macbeth makes it look like the drunk servents did it.
Macduff then arrives and goes into the kings' room to find him murdered. Macbeth then goes in to see and when he comes out he says he saw the servants with their bloody daggers and got so mad he just killed them right there.