Back in the ’80s, the film critic John Simon devised a classification system that neatly explains why Woody Allen’s comedies charm disparate audiences. “A highbrow moviegoer can laugh,” Simon wrote, “a middlebrow, empathize; a lowbrow, gape, awestruck.” Something similar could be said about the appeal of Dan Brown’s novels. The highbrow can chuckle condescendingly at their supposed erudition. The middlebrow can engage with them in earnest. And the lowbrow can simply marvel. There is something for everyone.