The key to unlocking any cinematic mystery worth chewing on—like, say, how Rian Johnson crafted an old-school, Agatha Christie-indebted whodunit as crisp and crowd-pleasing yet politically urgent as Knives Out—is to first assess what we do and don’t know. First, there is how the writer-director (of Brick, Looper, and most recently before this, Star Wars: The Last Jedi) assembled his rogue’s gallery of suspects.