I was rereading the passage in Blood Rites where Harry has his soul gaze with Thomas and has a conversation with Margaret.
She tells Harry something about Thomas, the Hunger Demon, and Justine that caught my eye.
Blood Rites, page 171
Margaret doesn't say that Thomas thinks she is gone. She doesn't say, Believes she is gone.No, she says quite clearly that Justine is gone. Maybe I am just splitting hairs here, but it seems to me that Margaret isn't beating around the bush here, Justine is gone, as in dead. You might ask the question about how would she know for sure? Which is a good question, but Margaret also says that the Hunger Demon in Thomas knows. So if Margaret meant that Justine was indeed dead, could this be the moment when Nemesis made it's entrance? Also there is a reason for the Hunger Demon to go along, if it is connected to Outsiders. Anyway, if I am right, Thomas did kill Justine after all in Blood Rites, and then her body was taken over by Nemesis, the Hunger playing along. Nemesis needed years to get all the chess pieces in place, years to manipulate Thomas into striking when he did. Nemesis needed Justine's body for that, needed to be Justine to manipulate Thomas into the events that led to Battle Ground.
It's an interesting notion.
But before analyzing too deeply, I want to ask: what -- not
who, but
what -- was Harry talking to?
I had been presuming a sort of pre-programmed simulacrum, a miniature "spirit of knowledge" along the lines of Bob (or Lash & Bonea (and likely the Archive)) that Margaret had constructed for Harry before her death; albeit a vastly-lesser one.
But for this thing to be tracking all sorts of extra info -- Thomas, and Thomas' girlfriend -- happening out in the world, it'd need to be considerably more robust, not just pre-programming. Able to conduct reconnaissance, to learn, to adapt... not really "lesser," in fact quite robust.
The "robust" examples -- that we we know of for sure -- are all the work of a much-more-competent & powerful entity than a WC wizard with just a century or so of lived experience... particularly since we already know that her amazing & impressive "best skill" is with the Ways & with faeries. For her to also have stunning (& centuries-beyond her justified skills) degree of experience constructing spirits-of-knowledge would seem to be unlikely.
Which leads me to the next option: it really
was his mom... her "ghost" or "spirit" or "soul" or etc. And exactly how
that could happen is entirely unexplained... unless she's explicitly working in Uriel's "Spook Service" with Captain Murphy, Carmichael, etc?
But I repeat: before speculating on "what did Margaret mean by that," I'd be looking at "what even
was that thing, presenting itself as Margaret??!?"