Fix is an undeclared changeling and is the Summer Knight. Likewise, Lily was an undeclared changeling and Summer Knight and then Summer Lady.

I'll throw this out there too. Harry owes Mab a favor, plus, he's the Winter Knight, which means he owes all of the Winter Queens unlimited favors, excepting only that he doesn't have to accept any that would hurt the ones he loves.

He also owes Molly a favor from bargaining for the ring in Peace Talks. She warned him to not make an open-ended deal with the fae, but Harry's is remarkably dim in foresight.

Harry owed Lea a debt, and somehow, Mab wound up owning that debt. It's possible she ordered Lea to surrender that debt to her. We don't know what went on behind the scenes. Mab could do the same with Harry's debt to Molly.

Harry's favor to Mab is a conditional, he doesn't have to accept the favor asked. But Molly's debt has no conditions attached to it.

To say nothing of the fact that she could always order Molly to kill Harry. Harry might not have any choice but to kill in self-defense.

My theory is that there's another influence outside the fae courts that stops the fae queens from killing mortals.

Forgive me if this is kind of obvious, but...

Harry made a deal with Lea for power prior to the series beginning.

In Summer Knight, Lea traded the debt to Mab. Mab and Harry negotiated the debt could be settled by Harry performing three services. Mab states that the first favor is to find the killer of the Summer Knight.

At the end of Summer Knight, Mab offered to cancel the debt in exchange for Harry taking up the Winter Knight mantle. Harry refused, two more favors were still owed.

In Small Favor, Mab tried to collect on the second favor. Harry balked. Mab again offered to cancel the debt in exchange for Harry taking up the Winter Knight mantle. Harry performed the favor, finding Marcone. At this point, Harry still owed Mab one favors.

In Changes, Harry approaches Mab with a deal to accept the Winter Knight mantle in exchange for her healing his broken back, give him power to rescue his daughter, and that she not force him to kill anyone he loved. Harry fails to mention anything about the third and final favor.

Mab can't order the Winter Knight to kill, say, Molly. (Like she's ordered the Winter Knight to kill Maeve) But she could require Harry Dresden to kill the Winter Lady in order to fulfill the third favor.

Sword of Damocles, indeed.

Let's agree that Uriel is immortal as long as he retains his grace.

Harry's already been halfway to the other side, a soul is immortal.

Being unaging and naturally deathless is not the same as immortal. Mab is not immortal. She was not born immortal. She became immortal when she took up a fae mantle.

I'll refer you back to Bob's words in Cold Days. After about a decade, the person is lost behind the mantle. We've seen glimmers of this with Molly. Maeve entered Harry's birthday party bucky bare-assed. Molly did her "Welcome to the Jungle" entrance in Battle Ground clad only in frost. I'll be interested to see if Molly starts taking on Maeve's crazy, cock-tease personality.

Mab has been the Winter Queen for almost a thousand years. The mortal Mab can only peek out from behind the mantle on the Summer Solstice, when Winter has its weakest hold on her. She is mostly mantle at this point. Very little of Mab remains, on a day-to-day basis. But there has to be something left. Perhaps that's why the prior Summer Mother resigned?

In any event, Butcher's going to tell this tale sooner or later.

After the wedding Harry will no longer have protection from Lara. The wedding vows are a spell that removes true love protection. See Something Borrowed for confirmation.

Choice plays such a big part in mortal affairs, that stripping someone of their free will by saddling them with a mantle seems sure to draw down the response of The White God.

Especially if we find out at the end that it was Hecate evading TWG's edict to give up their immortality or withdraw from the mortal world. My theory is that she did both, and didn't. We'll find out when Mother Winter (Hecate?) spills the beans.