Robert Langdon, the long-suffering but durable Harvard professor who is the protagonist in The Da Vinci Code and several other Dan Brown novels, has a thing for Harris Tweed. No, make that passion, verging on obsession. At one point in Brown’s new novel, Inferno, Langdon discovers another character sewing a secret pocket into his jacket. “The professor stopped and stared as if she had defaced the Mona Lisa,” Brown writes. “You sliced into the lining of my Harris Tweed?” Langdon erupts in what may his most emotional moment in the entire novel.