For (Levi) Grossman, no books feel more like home than C. S. Lewis’s Chronicles of Narnia, which provide the template for what he likes to read—and how he wants to write.

it’s the way he uses language—which is nothing like the way fantasists used language before him. There’s no sense of nostalgia. There’s no medieval floridness. There’s no fairy tale condescension to the child reader. It’s...