Really didn't expect the Gemini thing hahaha, and nice switch up on the glasses lol
At first, I thought it was weird the that the still alive Gemini killer didn't know about his brother going to meet Dexter, but thinking about it, the Gemini brothers must have minimal contact as they only seem communicate through meetings scheduled through weird bookmark appointements.
The still alive Gemini must be the one who put the bookmark in the book in the first place.
Also, they really did make Mia's stay as short as possible huh, with perfect timing as well.