When I called up Danny Elfman on a Friday afternoon and asked what I was pulling him away from, he implored me not to laugh. “A violin concerto,” he said—which didn’t seem particularly laughable—and then, after a pause: “And the soundtrack to Fifty Shades Darker.” But I wasn’t about to laugh at the celebrated film composer, whose 80-plus credits include the scores to Dick Tracy, Mission: Impossible, Men in Black, the early-2000s Spider-Man movies and, most recently, The Girl on the Train.