Detective story character

[alsterellie]

What was that one detectve story which had a character who not only loved reading detective stories, but would also know the murderer before the clue was solved everytime? I think he (or she, I’m not sure) made pencil notes in the book while reading. These notes were either marking things which would later be crucial for solving the mystery or only something like answers to things that the sleuth in the book would figure out on that particular page, remarks like “See!” and “Told you so!”. I don’t remember if he or she solved the “real” crime in the story, but I rather think he did.
I have a feeling that was a story by Agatha Christie, though without Poirot or Miss Marple, but I'm not sure about that.