I think a minor character will get caught in the last episode after they dig the floor up, I’m going for the DS that looks like Dot, then that will lead on to the overall leader in the next series, Osbourne maybe.
It was Nesbitt, it was filmed at a marina in Belfast and if anyone asked they said it was for a photo shoot, I assume he was filming Bloodlands around there at the time.
I’m guessing that the undercover police officer has gone off the radar as they are about to find out the identity of H which they will offer to trade in the final episode.