When I think about the Arctis Tor stuff, I keep coming back to Jim's comment telling us to think about the primary and secondary effects of Molly's abduction, and also about Jim's hint that Mab never foresaw Harry throwing Summer Fire into Winter's Wellspring. The latter would indicate that drawing Winter's forces back from the border was never Mab's intention, so it was also never her intention to allow Summer to retaliate against the Red Court.
So, what would've been the effects that she did expect to happen? Until Harry sicced the fetches on Molly, he didn't even know she was the wizard who was acting as their beacon on the Earth side. Going back further, the fetch attacks were what ultimately caused Molly to bring Harry in in the first place. Just prior to that point, Harry was gearing up to use Little Chicago to hunt down the source of the black magic-- a broken Little Chicago, which would've fried Harry's mind like a 10 cent fuse in a thunderstorm.
Could Mab possibly have foreseen events clearly enough that she could send fetches ahead of time, have them maul a random guy in a bathroom just to set up Molly's boyfriend, and trigger Molly to call Harry just in time to prevent him from using Little Chicago and frying his little wizard brain?
We know that, as of Harry's conversation with Mab in Dead Beat, Lea was unable to come to the phone and Mab was taking her calls and responsibilities. We know that for Harry's entire life, Lea has followed him in the Nevernever, set up base across from wherever he was, and guarded him from attacks via the Nevernever. It's not much of a leap to guess that this would also have allowed Lea the opportunity to enter Harry's home from the Nevernever if she wished to do so.
We know that when Harry went to Arctis Tor, Lea was still detained, which would mean that Mab was still acting in Lea's stead. I think we have to assume that, in addition to Lea's other responsibilities, Mab was forced to take up guardianship of Harry's residence on the Nevernever side while Lea was absent. Mab would've been the one guarding Harry's home from Nevernever predators-- admittedly, with the aid of Lea's giant centipede and murderous tulips and such. Mab would've had perfect access to Harry's home, and maybe even a certain right to enter, given Lea's responsibilities toward him.
In short, Mab might have been able to foresee that Harry was about to use Little Chicago and get himself killed. She was under obligation to protect his spiritual self. It's unclear(to me, anyway) whether or not this would obligate her to protect him from blowing himself up with magic. What is clear is that Mab had personal reasons to want to see Harry protected, as evidenced by her refusal to get rid of Lloyd Slate until Harry was ready to take his place. So, Mab sends a fetch to mess up the orphan kid's life, Molly calls Harry just in time to prevent him from using Little Chicago, Harry heads out to meet Molly, and by wild coincidence he finds himself already on the trail of the black magic that the Gatekeeper sent him to hunt down. Eventually, Harry goes back home and grabs Bob, and while they're out Mab goes and fixes Little Chicago.
This theory might even explain the car that drove Harry off the road. It could've been one of Mab's servants, under orders to slow Harry down so that events would play out in the right sequence.
Still, as nice as all that is, it doesn't explain why Molly would've been abducted. The abduction actually forced Harry back to trying to use Little Chicago, which had by then been fixed. It also doesn't explain why the Scarecrow attacked Harry and Thomas outside of the Fool Moon warehouse. Unless the Scarecrow and the abduction were a distraction, maybe? Something to keep Harry's mind off of Madrigal Raith and what he was doing in Chicago? But no need to bring Molly all the way to Arctis Tor, unless Mab wanted Harry to see what had happened there. The bones of an army of trolls and the smell of Hellfire.
Maybe Mab was accomplishing multiple small goals all at once, and Harry ended up throwing something unexpected into the mix when he sent the Fire into the Wellspring.
Which still doesn't tell us why Sandra whatshername would have manipulated Molly into using black magic, or what Madrigal was supposed to do in Chicago. Although, given the common factor that both parties involved were using magic to instill fear, maybe the two were connected. I have no idea how they might've been connected, I'm just taking a wild guess here.
On the other hand, why would Mab have gone to all that trouble rather than just popping over and fixing Little Chicago at the start of the whole mess? I dunno. Maybe she didn't want to be seen by Bob, or maybe she saw an opportunity to accomplish other goals at the same time, or...? Anyway, it's just a theory.
