There's a Catch (it has to be a bargain) CD's Spoilers

[GrandPanjandrum]

This Nemesis character is getting credit for everything, and in my opinion it's not the end all be all of antagonists.  I think there's a catch for Nemesis to infect an immortal.  I think Nemesis has to strike a bargain for the infection to take:

Lea:  In Proven Guilty she points out that she got too arrogant with her power and thought she could beat the "he who stalks us all."  In other words, she welcomed Nemesis to try and take her as part of accepting the Morgana Athame.  She thought she could defeat him...but learned differently.

Maeve:  Maeve was toturous, sadisdic and viscious towards mortals (mostly) because she was envious of their free will.  She, so much, wanted what they had, and took every oppotunity to exercise her anger in that regard.  Then, she bargained with Nemesis for free will, and planned on using it to lie to Harry so that he killed Mab, and she took the throne.  Even at the very end, she accuses Mab of being envious of her free will

Aurora:   I believe Aurora initially resisted Nemesis' bargain.  However, allies of the Outsiders discovered a 'mortal' child named Allison Ann Summers (born just before Grave Peril).  Bianca and others caused the thread between Faerie and Reality to thin, allowing a misled Agatha Hagglethorn to specifically make claim on the infant.  The infant turned out to be Aurora's.  You will recall that she has a remarkable amount of mortal/changling acquaintances (brought to light in Summer Knight).  Harry was able to save Allison Ann Summers in Grave Peril, but it was a close thing.  Nemesis used this to convince Aurora to accept the infection, and her ultimate goal was for Winter to hold dominion such that she would be able to walk off into the snowy sunset with her child.

Cat-Sith:   Not knowing this character too well, it is difficult to understand what would motivate him to disavow his Queen.  However, he is the leader of an entire species.  It must be demeaning to take orders from another regent.  Especially, it must be demeaning to be ordered to take commands from Harry Dresden.  And, considering the first time we see him after the infection, he tries to kill Harry.  And, considering that he stated how much he wanted to make coasters from Harry's spine in the beginning.  I think Cat-Sith was promised the opportunity to kill Harry Dresden (an instinct) if he accepted Nemesis.  Even so, Cat-Sith resists to some extent.

[Tamar]

Aurora:   I believe Aurora initially resisted Nemesis' bargain.  However, allies of the Outsiders discovered a 'mortal' child named Allison Ann Summers (born just before Grave Peril).  Bianca and others caused the thread between Faerie and Reality to thin, allowing a misled Agatha Hagglethorn to specifically make claim on the infant.  The infant turned out to be Aurora's.  You will recall that she has a remarkable amount of mortal/changling acquaintances (brought to light in Summer Knight).  Harry was able to save Allison Ann Summers in Grave Peril, but it was a close thing.  Nemesis used this to convince Aurora to accept the infection, and her ultimate goal was for Winter to hold dominion such that she would be able to walk off into the snowy sunset with her child.

That is a compelling theory considering how we never got any information about Allison after Harry's Hospital visit.

[Dimitri]

Cat-Sith:   Not knowing this character too well, it is difficult to understand what would motivate him to disavow his Queen.  However, he is the leader of an entire species.  It must be demeaning to take orders from another regent.  Especially, it must be demeaning to be ordered to take commands from Harry Dresden.  And, considering the first time we see him after the infection, he tries to kill Harry.  And, considering that he stated how much he wanted to make coasters from Harry's spine in the beginning.  I think Cat-Sith was promised the opportunity to kill Harry Dresden (an instinct) if he accepted Nemesis.  Even so, Cat-Sith resists to some extent.

I would say that it needs some consent to really work but that anyone can be taken, I think Cat Sith was taken, not given, which is why Cat Sith seems less effective than he should have been. Those that give consent become agents of Nemisis, those that are taken become puppets.

[Serack]

The question of how nemesis spreads is an important question that we really don't have a lot of data on.  I think that the closest parallel we have is the Denarians.  And for that, it seems that the infected just has to pick up the coin for the infection to start actively tempting.

Aurora:   I believe Aurora initially resisted Nemesis' bargain.  However, allies of the Outsiders discovered a 'mortal' child named Allison Ann Summers (born just before Grave Peril).  Bianca and others caused the thread between Faerie and Reality to thin, allowing a misled Agatha Hagglethorn to specifically make claim on the infant.  The infant turned out to be Aurora's.  You will recall that she has a remarkable amount of mortal/changling acquaintances (brought to light in Summer Knight).  Harry was able to save Allison Ann Summers in Grave Peril, but it was a close thing.  Nemesis used this to convince Aurora to accept the infection, and her ultimate goal was for Winter to hold dominion such that she would be able to walk off into the snowy sunset with her child.

I don't know that I have ever seen a theory like this.  Reallllly interesting idea.

[Tamar]

I don't know that I have ever seen a theory like this.  Reallllly interesting idea.

The child's last name is Summers after alll.... And didn't Mab use the name Sommerset or something like that in Summer Knight?

[TheCuriousFan]

The child's last name is Summers after alll.... And didn't Mab use the name Sommerset or something like that in Summer Knight?

Yep, she uses the Ms Sommerset name.

[GrandPanjandrum]

I guess I should add, although it might not be important:

Allison Ann Summers, I think, was born right around Halloween.  If Winter and Summer are all about balance, then Summer would, also, want an "entity" able to effect the Outsiders.  As we don't know the particulars of her birth, there is no reason to suspect that she was to be Summer's Child of the Stars.  But... it's possible.  Considering the unique things happening around that time (thinning of the thread), there's a chance that the timing is unique astrologically speaking.

[Tami Seven]

I guess I should add, although it might not be important:

Allison Ann Summers, I think, was born right around Halloween.  If Winter and Summer are all about balance, then Summer would, also, want an "entity" able to effect the Outsiders.  As we don't know the particulars of her birth, there is no reason to suspect that she was to be Summer's Child of the Stars.  But... it's possible.  Considering the unique things happening around that time (thinning of the thread), there's a chance that the timing is unique astrologically speaking.

The year of birth might be as important as the day, still isn't that around the same time Little Harry Carpenter was born?  Maggie's birthday is in November IIRC,  but in a different year.  Have no idea what the rule is.  So this child, Allison, may not even qualify. 

[pharthead]

I really like this idea.

I like the idea of Nemesis being like the fallen.  You could take that a step farther, in that nemesis gets into your head the second you come into contact with it.  Then it sits dormant for a short time shifting through your memories and offers you something that you want. 

In some cases, Nemesis can't offer something, or you refuse its offer, in which case nemesis makes you a puppet.  I assume that Lea and Cat Sith are in the puppet category.  Also, Nemesis is extremely powerful (it took Mab years to get it out of Lea) so he would have the power to alter people. 
I would assume that Cat Sith fought with Nemesis at first, and then pulled a common Malk attribute when fighting things stronger than it and ran.  In this case, it ran and hid in a far corner of its mind, and tweaked Nemesis's elbow when doing things.  It explains why Cat Sith was moving so slowly in the beginning of the battle on the boat.  Nemesis didn't notice something was jostling his arm until Dresden called attention to it.

[maurlysander]

I think that there also maybe some ritual, or choice of rituals, that takes place to infect someone.   I think one of the possible rituals is involved in sex magic and that is why Maeve wanted to seduce Hunt-Master Harry so bad throughout the whole series.  I think Lea using the Dagger infected her, and she infected Maeve.  That means there are two ways of being infected.  Contact with an infected magic item. Some sort of contact with an infected person.  However it seems it requires more than just casual contact.
I also think that Nemesis, a thinking being, is somewhat selective in its process of who it infects and probably doesn't just go after every small fish in the sea.  The spectrum is that there is all kinds of carriers that only are triggered if they need to be.  Kind of like a magical Manchurian Candidate type thing.

[Elegast]

The infant turned out to be Aurora's.  You will recall that she has a remarkable amount of mortal/changling acquaintances (brought to light in Summer Knight).  Harry was able to save Allison Ann Summers in Grave Peril, but it was a close thing.  Nemesis used this to convince Aurora to accept the infection, and her ultimate goal was for Winter to hold dominion such that she would be able to walk off into the snowy sunset with her child.

That a really great idea.

Here comes another wild guess:

Slate gave me a cold smile. "That old bastard Reuel's power, for one thing. I'll be twice the Knight I was before-and then I'm going to settle some accounts with that little bitch Maeve." He licked his lips. "After that, Aurora and I will decide what to do next."

Suspicion grew in his gaze, but Aurora laid a hand on his shoulder. Slate's eyes grew a little cloudy at her touch, and he closed them. "Peace, my Knight," the Summer Lady murmured. "The wizard is a trickster, and desperate. He would say anything he thought might save him.Nothing has changed between us."

Maybe Slate was the father.

[GrandPanjandrum]

Here comes another wild guess:
Maybe Slate was the father.

Ok...now that's disturbing...but feasible.  I couldn't find my copy of Summer Knight, or I would have gone hunting for something like that myself.

[Elegast]

“These mortal notions,” Maeve said. “Good, evil, love. All those other things your kind natter on about. Are they perhaps contagious?”

I rose with her, politely. “Some would say so,” I told her.

She grimaced. “In the time since her death, I have often thought to myself that Aurora was stricken with some mortal madness. I believe the Queen of Air and Darkness has been taken by a similar contagion.” She suddenly shuddered and said, voice curt, “I have answered you with truth, and more than needed be said. Does that satisfy the accounting, mortal?”