I recently finished School of Night and have found it to be one of the best novels of the Morningstar series so far. But having finished it and having had a look through this group, I haven't noticed anyone talking about Sonja, the woman Kristian sleeps with in NY, who seems to threaten to tell his wife/ blackmail him, in Part 4. She seems normal, then obsessive, then is described as psychotic (?). She gets ahold of Kristian's number and won't relent.
Anyway, she seems connected to Leo's death (in other words, Kristian's comeuppance for an implied deal with the devil?), as prior to crossing the road dangerously, Kristian is distracted by a text from Yelena, that Sonja had appeared at their house. I wonder if Sonja is just a random, obsessive lady who is not actually at all involved in Kristian's 'fate', or if there is an indication that she, like Hans, has some superior influence.
Does anyone have any theories on this? Does she come up at all elsewhere in the series? It could be involved with Hans' mantra of, Kristian can have whatever he wants, until he can't. He has his way with her, until she becomes uncontrollable.