They are accused of 'plotting' the assassination of the prime minister. = They are accused of 'plotting' to assassinate the prime minister.
As the 'plot' unfolds [=as the story continues; as things happen in the novel, movie, etc.], we learn more about the hero's family.
He is a master of 'plot' [=he is very good at thinking of interesting stories], but his characters are not realistic.
(..) Mrs. Thorwald. You haven't spent much time around cemeteries, have you? Mr. Thorwald could scarcely put his wife's body... in a plot of ground about one foot square. Unless, of course, he put her in standing on end. Then he wouldn't need a knife and saw. (..)1954 Rear Window