Well, I found the notebook today. It was laying just outside my front door. I think that rules out having just "misplaced" it. And, by extension, brings up the real possibility that Red broke into my house for the sole purpose of getting back Mike's old insanity-journal. And I had no idea he was even there.
Wait, it gets better. I checked, and there's more writing here than there was before (I'll upload some pictures later).
So, Red broke into my house, stole Mike's old notebook, wrote in it, and gave it back. Fairly obvious question here, but... Why? I'll read look over the new stuff some more, but I don't think that it'll tell me why this guy broke in.
Also, I have a gun. Just throwing that out there.