World-building is one of the most difficult parts of writing a world that differs in any way from ours. It’s easy enough to figure out the main changes, like “magic works” or “dinosaurs are still around”—you probably have them in mind from the beginning, or odds are you wouldn’t be writing that particular world—but then you have to think about what smaller changes they’d cause. Do the people in your world have surgeons, or does magic solve all health issues. If not, why not? How does the freeway system adapt when people are riding stegosauruses? And so on. That’s hard. It’s also a lot of fun—like putting together a puzzle, but generally without that moment when you realize that the dog ate three of the pieces. When I was writing NO PROPER LADY, I got to do two separate and intertwined pieces of world-building. One was Simon’s world, which was 1888 as we knew it on the surface—only with all sorts of secret knowledge and magic underneath. (I drew a great deal on actual occult societies of the time, though I took considerable liberties in the service of fiction.) The other was Joan’s world: a world very different from either…