Way back in Storm Front, we had the Three-Eye drug, which turned out to be a potion that really did grant the Sight to vanilla mortals. Victor Sells supposedly created it, but he was an untrained hack. What are the odds that he could have developed something that no White Council wizard had ever heard of before? Or at least, something that was not common knowledge among wizards. I think Victor Sells probably got the recipe, or the beginnings of it, from someone else. Probably someone in Maggie's original group.

And then we have Kumori, in Dead Beat, talking about eliminating death forever through necromancy. Harry himself thinks that this would do more to level the playing field between vanilla mortals and wizards than practically anything else, making their lifespans equal to a wizard's for the first time in history. If she and Cowl were successful, then combining that with a safer version of the Three-Eye drug, that would eliminate the Sight and the longevity from the list of disparities between vanillas and wizards.

Well we know that he was using a black magic ritual that was a smaller version of the RC ritual in Changes.  So who taught him the ritual & how to make the drug?  Was it Ariana or someone else (Black Council) using a cat's paw?

Yeah.  It does make more sense that she is Marcone's.  What about some other entity?  I think that it is too easy for it to be just Marcone.  Maybe I'm looking for connections where there are none.  But she was way out of Marcone's territory to be enlisted into his employ I think.  Maybe some one we haven't seen.  If you learned how to turn into a wolf, would you stop even if your group of friends grew apart.  Maybe she got into some messy shiznit in California (I think that's where they said she was.)  That would also be a great reason to pick up & leave

Where was Michael? Where was… anyone?

Cassius leaned down and said, “And when I start, Dresden, I want to be free to indulge myself. To really let go and live the moment. I’m sure you understand.”

No one is coming to save you, Harry.

Two thing about this. 

• After "hearing this, Harry clearly gave up on a rescue & instantly became more cynical.  I think this was the last straw as far as he was concerned in giving Cassius any mercy.  Therefore it pushed him towards killing Cassius & giving him more guilt & getting him that much closer to "becoming a monster"
• Also, it could have been Lash that whispered it to help him on the path to corruption.  Remember, that it was a big deal for Harry later to have killed Cassius in cold blood.  He had trouble talking to Murphy about it & it was the first thing he talked about with Michael just before he confessed about the coin