Energized by the internet persona Q’s complex web of conspiracy notions about the forces aligned against President Donald Trump, Q’s followers have spread virally online and now, in real life too, forming a movement known as QAnon. From somewhere in the vast and mysterious “deep state,” a dissident agent rises up to give the people cryptic clues about how their heroic president will push back the forces of evil and make America great again. The renegade informant is known only as “Q,” and if he actually exists, it’s not as a character in a movie, but somewhere in the Washington,...