This series has Sally Lockhart as the protagonist --this character first appears in The Ruby in the Smoke, a play Pullman wrote for performance by a secondary school. In the play, sixteen-year-old Sally Lockhart attempts to investigate her father's apparently accidental death. In the course of her investigation she uncovers her father's connections to the opium trade, the Indian Mutiny, and a cursed ruby.
Philip Pullman was attracted to the story and characters so much that he rewrote the play as a children's book; he later extended the story into a series of four books.