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.
I do remember she told Rita not to reveal all at the beginning, not to tell the reader where the mystery is headed.
I agree with Janine, most writers that talk about their writing say a character takes command of their story and the writer lets the character go in the direction he (she) wants to go. This infers the control of the book is taken from the writer and has a mind of its own. This does not fit Horace’s style where he is always in control.