Holy moly, what a chapter! "Undercurrents" certainly is a fitting title, a whole bunch of threads of the past and present are all coming together and the various forces start approaching the point of (heh) moving out of the shadows. Even introduces yet another potential side:
Also, I skimmed through chapter 107 to see if there's anything else relevant there and there was - Kate's name actually comes from Catherine's pet name. If this guy is actually some original resident of the Mirrors House who somehow kept his memories and was close to Catherine he might actually be able to guess who Kate is.
Yep, particularly if he realizes (and he probably could from that briefcase and a bit of investigation) that she must have come from beyond the island. I hadn't really considered it before, but Kate is in fact the "legitimate heir" of the Household. There have been plenty of stories throughout history where even genuinely loyal attendants served new masters because they were convinced those they originally swore loyalty too were all dead and gone forever. But a Mirror turning back up might throw a wrench in the works if this guy is thinks he can restore things to the original family.
Of course an alternative darker path is just seeing opportunity in that Kate might have more potential then anyone as a completely native fusion from birth. If he's interested in overthrowing the GGF, or merely gaining more advantage, it's quite the card too.
All this will be fun in that it could be another piece of the puzzle Kate needs to solve to beat the adults. Even now she'd still have a hard time against a completely unified Adult side. Anthony being an agent and developing his own splinters inside is an aid, and now he has Unification fragments to work with. So is Patrick's powerful soot neutralization. Those still don't feel like enough though. But if the adults aren't unified and are capable of being split somewhat, that could really shake things up. Also if it's another link to the past might be a good excuse to give us some more insight into what happened at the very beginning of it all, and what went into getting things this far.