The film starts with the funeral of Macbeth and Lady Macbeth's child, with both parents grieving for their loss. The funeral is not in Shakespeare's play, nor does the play directly mention the death of a child, but in Act 1, Scene 7, Lady Macbeth says "I have given suck, and know how tender 't is to love the babe that milks me," so the loss of a child can fairly be inferred.
Macbeth, who supports King Duncan in the civil war, is leading royal troops into a final battle. Macbeth emerges victorious, but there are heavy losses, including many boy soldiers. The battle is observed by three women with a small girl and an infant. They approach Macbeth and Banquo, hailing Macbeth as Thane of Cawdor and future King, and Banquo as a father of Kings, before disppearing in the mist.
Elsewhere, Duncan hears about Macbeth's victory and is brought the Thane of Cawdor who, deemed to be a traitor because he has allied himself with the Norse invaders, is stripped of his title and executed. The King orders his servants to take the title of Thane of Cawdor to Macbeth, who reacts uncertainly. Macbeth sends a message ahead to his wife, Lady Macbeth, telling her about the witches' prophecies. Lady Macbeth then prays to the dark spirits in the village church, asking them for guidance. When Macbeth and his soldiers return, and her husband tells Lady Macbeth that Duncan will stay one night as their guest, she urges Macbeth to kill the King to fulfill the prophecy made by the witches. Duncan arrives at the village and a feast is being held, where the King pronounces Malcolm as his heir. Macbeth still hesitates and Lady Macbeth persuades him to commit the deed, while she slips a sleeping potion to the King's servants. After the feast ends, Macbeth sees a ghost of one of the boy soldiers who had been killed during the battle who gives him a dagger and leads him towards Duncan's tent. Macbeth brutally slays Duncan. Malcolm enters the tent and, seeing what Macbeth has done, flees in fear. Shaken, Macbeth goes to his wife and gives her the dagger he has used to kill the King. Lady Macbeth rebukes him, saying that he should have left them in the tent and she goes herself to place the dagger in the hands of the sleeping chamberlains. Later she meets Macbeth in the church where they both wash the blood from their hands and she tells him that the water has washed their deed away.
In the morning, Macduff enters the tent to wake Duncan, only to discover that he is dead. Macbeth summarily executes the sleeping servants to prevent their denial of the murder. Macduff and Lennox, a Scottish noble, discuss that as Malcolm has fled to England that puts him under suspicion of being involved in the murder. They also admire Macbeth's justice on the supposedly-treacherous servants in the rightful fit of anger. With Malcolm gone, Macbeth is asked to become King of Scotland. After the coronation he sits in a sour mood in his chamber where Lady Macbeth comes to him. He complains that killing Duncan was for nothing as Macbeth has no heirs to inherit the crown which will pass to Banquo and his son, Fleance, according to the prophecy. He invites Banquo with his son to a banquet and finds out that they both plan to leave. As Banquo is becoming suspicious, Macbeth sends three assassins to murder him. Banquo is killed, but Fleance escapes to the woods.