After Duncan has retired for the night, Lady Macbeth concocts a plan with her husband to murder the king. She will drug the king's chamberlains and then Macbeth will kill Duncan while he sleeps. She is determined to go ahead with the plan, even if she has to do it herself:
> But screw your courage to the sticking-place,
>And we'll not fail. When Duncan is asleep,
>(Whereto the rather shall his day's hard journey
>Soundly invite him,) his two chamberlains
>Will I with wine and wassail so convince,
>That memory, the warder of the brain,
>Shall be a fume, and the receipt of reason
>A limbeck only. When in swinish sleep
>Their drenched natures lie as in a death,
>What cannot you and I perform upon
>The unguarded Duncan? what not put upon
>His spongy officers, who shall bear the guilt
>Of our great quell? (I, v, 65-78)