There's a thread about Summer Knight foreshadowing which is about Aurora in SK and Morgan in his microfiction letter, both calling Harry a Destroyer. What I have to say here is related but goes off on a tangent that deserves a separate discussion.
I think that while Martha Liberty does not use the word Destroyer; with the hindsight we have from reading Morgan's microfiction and what Aurora said about Harry in Summer Knight, Liberty strongly implies that is exactly what she meant when she says of Harry to Ebenezer, "You know what he was meant to be." Also, Mother Winter described Harry as a weapon in Cold Days. The way I read this passage is that Mother Winter wasn't referring to Harry as a thug who would kill anyone who pissed off Mab, she was saying that Harry was a weapon that was created with a deeper purpose in mind.
So, for whatever purpose was envisioned for Harry, or whatever it is he is supposed to destroy, an awful lot of people know it. Apparently Margaret LeFay wasn't very good at keeping Harry's purpose a secret. It probably explains HWWB's interest in Harry when they first met and the reason why HWWBf kept saying "Send out the wizard" in Cold Days. The Walkers wanted to turn Harry's purpose and ability to their own advantage.
To follow this idea a bit further; in Blood Rites Ebenezer told Harry that he and Margaret argued over some scheme she was working on with Lord Raith, and possibly Duchess Ariana of the Red Court. Justin DuMorne was one of Margaret's associates so it seems likely that he was also aware of this plan. Though at present this is just speculation, it seems to me that a solid guess is that Harry's birth, the timing of it, and its exact purpose are at the center of this scheme.
So look at the list of characters; besides LeFay, Raith and Arianna, who have some knowledge of the plan: Ebenezer McCoy, Martha Liberty, Donald Morgan; and if he knows Arthur Langtry must also know, Justin DuMorne, Summer Lady Aurora, Mother Winter, Mother Summer, and probably HWWB. There are others who are also highly likely to be in the know, such as the Leanansidhe, Mab, and Titania. This list might also be extended to Ancient Mai, Aleron LaFortier and the Gatekeeper. Finally, Captain Anastasia Luccio should be in the know. You would think the head of the wizard's secret police would find out, whether or not the Senior Council would have officially informed her.
What I want to know is how did they all find out? Did Ebenezer have to make a report to the Senior Council about this diner and what was said there? That would explain the Senior Council members knowledge. I could see Lea finding out directly from Margaret LeFay. Justin may have also found out from Margaret or he may have had a hand in the planning. It doesn't explain how the Summer and Winter Mother's, the Queens and Summer Lady found out. It's possible Maeve was too lazy to keep herself informed, but then again perhaps she knew as well. I suppose HWWB could have found out from anyone with knowledge of the plan who became nemfected.
When is Harry going to start asking questions about this? I really hope Ebenezer has another conversation (or three) with Harry in the next book so we can start to get some answers. Does anyone want to take a guess about how knowledge of the plan spread or guess at any other characters who may know; or might have known before their demise, about Harry the Destroyer?