Having succumbed to the lure of evil in the enticement of the three weird sisters, Macbeth becomes increasingly irrational, underscoring their chant of "Fair is foul, foul is fair." When Macbeth visits the witches in Act IV, the first witch tells him he should beware of"the thane of Fife." Then, when he learns that Macduff has gone to England, Macbeth, who is becoming increasingly paranoic after visions of Banquo's ghost and the troublings of his guilt, decides to kill the family of Macduff because the second witch has shown him a procession of kings and Macbeth is aware that Macduff may suspect him of having murdered Duncan since Macduff has suggested his suspicions after he arrives at Macbeth's castle in Act II. For, he declares that he will fight against the "treasonous malice" (II,iv,133) of which Banquo speaks.
Of course, after Macduff learns of Macbeth's heinous act of murdering his family, he vows revenge upon Macbeth. Fulfilling the prophecy of the witches, they meet at Dunsinane and Macduff, informs Macbeth "Macduff was from his mother's womb/Untimely ripped." When Macbeth then tries to back out of the situation, Macduff thell him "yield thee, coward..." (V,iii,23). With brutalit, Macduff slays Macbeth and brings his head to Malcolm.