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.
(..) Once trusted by this Council... ...charged with maintaining the defense of the planet Krypton itself. Chief Architect of this intended revolution and author of this insidious plot... ...to establish a new order amongst us... ...with himself as absolute ruler. You have heard the evidence. (..)1978 Superman