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 Dobby had to come. Dobby has to protect Harry Potter. To warn him. Harry Potter must not go back. . . . . .to Hogwarts School of Witchcraft and Wizardry this year. There is a plot, a plot to make most terrible things happen. What terrible things? Who's plotting them? Can't say. (..)2002 Harry Potter and the Chamber of Secrets