Billie Eilish writes songs like fiction, with rich characters, larger-than-life storylines, and fantastic Hollywood endings. Using her exquisite soprano, the Los Angeles native adds shadowy intrigue to classic subjects like first love and fast cars: “I’m biting my nails / I’m too young to go to jail / It’s kinda funny,” she coos on “Bellyache,” a thrilling peek into the mind of a killer.