This idea just occurred to me during another discussion on the forums. I think a fair bit of evidence, taken together, suggests the possibility that Id Harry and Mab struck a bargain at the beginning of Small Favor. To be clear, by "Id Harry" (IH) I mean the version of Harry in his subconscious, dressed all in black.
First off, was this even possible? Let's examine means, motive, and opportunity:
Means: Molly states in SG that she talked with Id Harry when she was in his head getting Bonnie out, so it seems entirely possible to me that Mab could have met with him when she was in Harry's head.
Motive: IH has shown three primary motives to date: Harry's survival, getting laid, and "protect the offspring." Mab certainly could help with those, by granting him the power of the Winter Knight. And it has the added benefit of making Harry's Id impulses much louder and more powerful
Opportunity: Mab has been inside Harry's head at least once undeniably, at the beginning of Small Favor, after which he cannot remember his blasting rod.
So, it
could have happened. What's the evidence that it did? The original basis for this theory grows out of an idea by Ms Duck that has a "Strong Evidence" label on theories list, and can be found
in post 2 here.
Small Favor
Now this is where life gets interesting. Mab outright (she admits it) takes Harry’s blasting rod and then makes him forget she took it. What she leaves behind is the image of a tarp, and a splitting headache. SF 212:
“pain stabbed into my head, ice picks plunging into both temples. I flinched and doubled over. Blasting rod. Familiar words. I fought to summon an image of what went with the words, but I could not find anything. I knew the memory associated with those words, but try as I might, I couldn’t drag it out. It was like a shape covered by some heavy tarp…”
The second thing that happens in this book is Harry meets the isle for the first time. There is also a small in-joke here; when researching gruff, harry find a Calvin and Hobbes book. For the non fans, the last strip of the comic had Calvin ( the too bright smart alleck) and Hobbes ( his wiser but snarky and horny friend only he can talk too) head off into a eternal winter wonderland of snow, magic, and snow goons. (yes, Mab left him a book)(that has a beware of Hobbes in joke)
Turn Coat and the two clue bats:
The first clue is on page 211
After Thomas is taken, Harry searched for him magically, but never uses or mentions Little Chicago. (although damaged in WN, it is fixed by this time, note SJ).. all he describes is:
Quote
“a long table in the center of the room is covered by a canvas tarp.
Now it is important that not only does he not mention it ( he does in every other book, whether he uses it or not, he is very proud of it.) but Bob does not mention it either. And almost the very first thing he mentions in the books is his splitting blinding headache.
The second clue is on page 215
Mouse come over to talk to him, gets Harrys attention, and then when Harry bends down, harry gets a second blinding headache, and loses his train of thought. This is important because it is shown later that Mouse could have found Thomas, and he certainly believed he was a match for shaggy, or at least that harry and he together were.So someone covered the table, removed the memory from Harry and Bob, and gave Harry a headache just in time to prevent him from rescuing Thomas.
Why would Mab do this?
Two possible reasons: First, she believes Harry and Mouse were not a match for shaggy, or she needed Harry to bond with Demonreach for another later purpose, and Thomas being in trouble was the goad she used to get harry to do something this drastic.
The clue bats she is referring to are a WoJ about two hidden clues in TC:
The clue bat is a tough thing to guesstimate. I mean, I hit y'all with at least two other major things in this book that no one seems to have picked up on at all, so far. 
tl;dr: Harry completely ignores Little Chicago in Turn Coat. He describes it as having a "tarp" over it, which is precisely the same language used to describe how Harry's blasting rod appears in his mind when he tries to remember it after it was taken from him by Mab.
In TC, right after the confrontation with Shagnasty at Raith Manor, Harry was down in his lab beating himself senseless over how he could find Thomas, and never thinks to try Little Chicago:
Two hours and a half a dozen attempted tracking spell later, I snarled and slapped a stack of notepads off a corner of a table in my sub-basement laboratory. They thwacked against a wall beneath Bob the Skulls's shelf, and fell to the concrete floor. "It was to be expected." Bob the Skull said very quietly.
He put time into trying to find Thomas with magic, but neglected to use his single most valuable tool for this sort of problem. He doesn't even mention it as an option, or even acknowledge its existence while running down a description of the room; only how there's a long table covered in a tarp. Ms Duck points out how out of character that is, Harry is immensely proud of LC and name drops it in every other book it exists in. Odder still, Bob is there with him, and he doesn't suggest using it either. It's had quite a few successful outings by TC, so why not?
We also have the "ice pick" headaches when Harry interacts with Mouse in the same period. Mouse also could have found Thomas (This is confirmed by Mouse later on). We know that the ice pick headaches are later identified as the psychic trauma of Bonnie straining in his head as she grows. In both cases, something going on in Harry's head shakes him off the quickest paths he could take to finding Thomas and Shagnasty. But how? And why?
As Ms Duck stated above, the upside of these "delays" is that Harry doesn't confront Shagnasty without substantial backup (and likely end up dead), and he shortly thereafter conceives of his plan to have a sanctum invocation on Demonreach. Both of these developments serve Id Harry's interests. They also serve Mab's goals, amassing power to her would-be Knight.
So, let's imagine a scene, at the beginning of Small Favor. Mab has entered Harry's mind, and is approached by Id Harry, who has the relatively recent task of watching over the newborn Bonnie. And Id Harry and Mab begin to deal. IH wants Harry's immediate survival, protection for Bonnie, and a chance to get laid. Mab wants Harry as Winter Knight, and also wants to earn Harry yet more power by guiding him into becoming Warden of Demonreach. So, the bargain is struck.
Id Harry will guide Harry ever closer to taking Mab up on her offer of Winter Knighthood, and towards a sanctum invocation on Demonreach. Both goals will aid in Harry's survival, amass power to help protect Bonnie, and being WK definitely ups the chances that Harry will finally have some sex. More generally, the WK mantle will increase IH's power over what Harry does, as it encourages Harry to pursue his more animalistic, base tendencies. To enable IH to help further with these goals, Mab will give IH the ability to hide Harry's memories from himself, as represented by the snowflake pin he now wears on his lapel. IH is responsible for hiding the blasting rod for most of SmF, at Mab's behest as part of this deal. He also prevents Harry from confronting Shagnasty directly in TC, by blocking out Little Chicago at a crucial moment and making sure Bonnie triggers a headache when Harry goes for Mouse. Instead he puts the idea in his head to take Morgan to Demonreach, and to perform a Sanctum Invocation. He is Harry's intuition, after all.
Mab will work towards Harry becoming the WK as well, and will see to it that Bonnie will be protected. She compels / arranges with Bob to get a vessel crafted for Bonnie, and to not point out how Harry is ignoring Little Chicago in TC. Furthermore, she helps guide Molly towards the skill level and power she will need to perform the "delivery."
The only bit of hand-waving I see in any of this is the timing on Bob being clued in / compelled, not to talk about LC. Mab could've done that at any point in TC though, Lea was still a Sidhe-sicle after all, so Mab could come and go from the lab as she pleased through Lea's garden, assuming she meant no harm. And Harry only goes into the lab the one time in that whole case.
It seems to hold together. You may begin poking holes, let's see how long it lasts.
