A general comment about Lea & the athame: We must remember that the athame itself is so powerful that it is considered to be equal value to Amoracchius. So let’s sidestep the Nfection for a second (we’ll get back to it).
Here is the sequence of events from Lea’s POV -
Lea gets Amoracchius in GP, however it is kinda useless to her due to its nature. Lea manages to exchange Amoracchius for Morgana’s athame, which is an artifact whose power can likely be tapped by a Sidhe.
Lea is probably supposed to turn over the athame to her Queen so as to not upset the balance, however being a power-hungry Winter Fae, she is tempted to see if she can use the athame to overcome “that which stalks us all”. She fails & is instead Nfected. The likely target of this Black Council ploy is Mab, with Lea having been incidentally Nfected (clearly not something Nemesis is opposed to).
By merely choosing to keep/ use the athame, Lea upsets the power balance in the Winter Court - Mab has to take away Harry’s debt in compensation (talk about equal value!) to balance things. I wonder if this seemingly ‘free-willed’ choice on Lea’s part is what told Mab she was Nfected?
@KurtinStGeorge
Exactly - we only see high-level elder Sidhe get Nfected in the series so far, so having C/D grade bad guys like Sells & Kravos also be ‘Nfected’ would somehow cheapen the danger posed by Nemesis.
It is also clear that Nemesis cannot spread beyond a certain audience - if it is spreadable over a larger audience, everyone would know about it thus defeating one of its’ greatest weapons. My WAG is that Nemesis can only possess 3 people at a time.
@Lady Inez & g33k
The purpose of Winter is protect the DV from Outsiders - this is why they have the power etc. that they do. My WAG is that post-BAT, the Outsider threat will be neutralized once & for all - when this happens, what becomes of Winter’s purpose? Without the looming threat of Outsiders, the Fae courts will lose a lot of their raisin d’etre & power. Perhaps they will no longer require Knights, thereby freeing Harry?