Well, Lady Mcbeth plots that she'll wait for King Duncan to go to bed because he'll be tired and then she will make sure to give the guards enough wine to sleep heavily so that they won't see/protect Duncan, that way Macbeth can sneak past and kill Duncan with the Guard's two daggers and once Duncans dead he will place the daggers near the guards so that they are accused-all of this in effort to become king