What mystery-writing advice does the author slip in that she, herself, observes? Are there any rules that she breaks?
I don’t think the author slips up. She appears to not break hidden rules of mystery writing. She gives clues throughout and somehow ends up surprising the reader at the end.
I personally don’t remember any unless it was in the way Horace approached his writing. The author does control the narrative but most author I’ve listened to usually tell of something that just takes over in the writing.