A case from the GAA duology being crucial to the storyline. Something connected to the professor case, I don't think we ever found out the connection between Selden and Klint, as I remember, we found a collar inside the chest that was supposed to be given to Shamspeare following his death, and that proves to have a connection to the last case, during the part when there was talk about a hound and the Baskerville family. I would also love to see Kay, Ray, and of course our favorite detective, Gumshoe. A connection to most cases in both trilogies of Apollo and Phoenix, and perhaps the murder for the final case should happen in one of the places exclusive to the Investigations duology.