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.
(..) but work on that clock. One day a letter came. Mr Gateau, done for the night, went up alone to bed. And their son came home. They burried him in a family plot where he would be with them when their time came. Mr Cake worked on his clock, laboring to finish. It was a morning to remember. (..)2008 The Curious Case of Benjamin Button