 Lady Macbeth makes her first appearance late in scene five of the first act , when she learns in a letter from her husband that three witches have prophesied his future as King . When King Duncan becomes her overnight guest , Lady Macbeth seizes the opportunity to effect his murder . Aware her husband 's temperament is " too full o ' the milk of human kindness " for committing a regicide , she plots the details of the murder ; then , countering her husband 's arguments and reminding him that he first broached the matter , she belittles his courage and manhood , finally winning him to her designs . 
