
The oath was this: “Do you promise that your detectives shall well and truly detect the crimes presented to them using those wits which it may please you to bestow upon them and not placing reliance on nor making use of Divine Revelation, Feminine Intuition, Mumbo Jumbo, Jiggery-Pokery, Coincidence, or Act of God?”
While I think we’ve all seen authors—well-known ones at that—break these principles regularly (after all, why can’t a ghost solve a crime? Or for that matter, a cat?), there was something to these expectations that made sense. A reader should be able to work out whodunit, at least after the fact, to be fair.

After all, there are many incidences of a community “solving” a murder when a corpse’s finger pointed to its murderer. Or when the corpse’s eyes would open and stare in the direction of the murderer’s house. There are even examples of a corpse bleeding from the nose or ears, indicating that the murderer was in the vicinity.
Sometimes, logic and reason and evidence would prevail and sometimes…they did not. There are many examples of superstitions, hearsay, and feelings making their way into court testimony, especially in ecclesiastical courts.

But I wanted Lucy Campion, my chambermaid turned printer's apprentice, to be someone who was resourceful and intelligent, despite having little formal education. But it wasn’t just about creating a character who would use her wits and evidence to solve crimes; I wanted her to question how the community identified murderers in the first place.
I also wanted Lucy to be someone who rejects the notion of providence as a means to explain murder. I wanted her to dismiss the idea that divine revelation could be a reliable way to identify a murderer—even if that meant challenging the expectations of her community.
I’d like to think that Lucy would approve of the Detective’s Oath.