I am confusion.
That shadow had a suitcase, did it come from outside?
That couldn't have been Kate either, since she knows that she started as a morph. Or hold on, maybe shadows do not actually start as morph, maybe the entire soot fairy thing is a lie and the great grandfather himself turns them into morphs! But well, that would kinda invalidate all the world building up until now, so not very likely I guess.
Very excited to see where this goes!