Lady Macbeth is Macbeth's wife and the mistress of the castle of Inverness, where King Duncan goes to sleep. She is the one who takes on the murder plan and, at the end, the one who appears sleepwalking, rubbing a bloodstain that will not come out.
In Act I, scene 5, she reads the letter in which her husband tells of the witches' prophecy, and she finds him too full of human kindness to take the short road. She calls on spirits to fill her with cruelty. In scene 7, when Macbeth backs down, she tells him that he lives like a coward and lays out the plan: to get the chamberlains drunk and place the blame on them.
In Act II, scene 2, she has drugged the chamberlains and left the daggers in plain sight. She says she would have done the deed herself if the sleeping king did not remind her so much of her father. When Macbeth returns shaken, she takes the daggers, stains the chamberlains with blood, and says: "A little water will clear us of this deed." In Act III, scene 2, now queen, Lady Macbeth is kept in the dark by Macbeth about his plan against Banquo: he tells her to stay ignorant and innocent until she applauds the deed. At the banquet (scene 4), she tries to cover for the ghost that only her husband sees, and she dismisses the nobles.
In Act V, scene 1, she walks in her sleep with a candle and says: "Out, cursed stain!" In scene 5, Seyton announces that the queen is dead. In the end, Malcolm says that, "as is believed," she took her own life.