As JB is a lazy writer, it makes sense for him to use the same possession methodology for Nemesis as he does for Denarians. We have seen Denarians operate in two ways.

1. Anduriel/Nicodemus work as a partnership. This parallels Nemesis/Maeve - Maeve was voluntarily working with Nemesis in exchange for freedom from her mother. Nemesis prefers this method.

2. Magog uses brute force to enslave the minds and bodies of his hosts. This parallels Nemesis/Cat Sith.

Now let's look at Harry and Lasciel. Through Lasciel's spirit, Lasciel attempted to form a cooperative (#1) relationship with Harry. However, as shown in Small Favor, Nicodemus believed that Lasciel would be able to use brute force (#2) to paralyze Harry long enough for Nicodemus to kill Harry.

My theory is that Mab is currently infected in the same manner that Harry was. When Mab touched took the Athame from Leah Nemesis was able to imprint on her. Nemesis is currently attempting to build a cooperative (#1) relationship. Mab is currently refusing and is too strong for Nemesis to simply take over like it did Cat Sith.

Why is this important? I think that Mab recognizes she can only prevail against Nemesis in the short term. Eventually, Nemesis will erode her defenses and start to take over. That is why Mab wants Harry as WK. We are vulnerable to ourselves. The Queens are Winter and the WK is part of Winter. Thus, while the Queens appear to control the WK, they are also secretly vulnerable to the WK. Mab needs a WK that will be strong and wise enough to exploit that vulnerability and kill her when she starts to lose control. One of Mab's goals in Cold Days was to start Harry on the road to discovering that the Queens are vulnerable to the WK. Harry now knows that the Immortal Queens can be stopped in certain places or certain times, and is on the path to learning that the Immortal Queens can also be stopped by certain people (i.e. their Knight).

This brings us to two possibilities. The first is that Harry will actually kill Mab, setting off the BAT. However, I think Harry is going to get around that and go with option #2. Harry will realize that it is Winter that is vulnerable to the Winter Knight, not the individual person in which Winter resides. Thus, Harry, will find a way to destroy the Winter mantle, setting Mab free of Winter. This will still set off the BAT, but it will create a touching scene in which Mab (and Molly) are restored to their humanity.

We know that JB originally outlined 20 case books and a 3-bok apocalyptic trilogy. Some of the case books, however, have involved threats that would at a minimum lead to an apocalypse, which leads us to he question of what will be the difference in the BAT. Here are my thoughts/theories.

The first line of Storm Front indicates that he case books are a narration of past events, likely from Harry's journals , similar to Merlin's and EB's as revealed in TC. I believe the last line of the last case book will mirror the first line of Storm Front. This will signify a shift in the BAT - they will either be narrated as current events or by someone who observed Harry during the events. Either way it leaves open the possibility that Harry dies in the BAT.

At some point Harry has to follow in his mother's footsteps and spend significant time in the NN. The perfect time for this to happen will be between the case books and the BAT. There are several ways this could play out - Harry could go to section of NN that moves slower, allowing him to gain vast knowledge in only few years of real time, or he could spend time in quickly moving areas, popping into the real world to save those with minor talent and becoming some kind of legendary guardian that nobody is certain is real or rumor. I like the latter idea better, but it is harder to reconcile with the idea that Faith kicks off the BAT in the last book. The latter idea also means that Murphy wouldn't be around for the BAT - but I could see a sacrifice by Murphy as the influence that causes Harry to withdraw from the mortal world into the NN before the BAT.