Drakul might run the Black Court vamps but he works much more like a White Court vampire. He has incredible power but appears to prefer deception, and misdirection than brute force. He prefers a small, elite group of members over a huge empire like the Red Court. He prefers to be invisible, until it's time to act. He prefers caution, to recklessness. He could have killed LTW, and River Shoulders, but the plan was falling apart, and he chose to exit the scene rather than risk staying, and fighting.
I suspect that the White Court didn't know the weaknesses of the Black Court, but Drakul did. I think that Drakul's son's ambition led to the Black Court getting far to big, noisy, and powerful. They were drawing the attention Drakul didn't want, but more than that they were growing too powerful for him to control. So he slipped the information on how to defeat them to the White Court. This would allow their large numbers to be eliminated, leaving only the strongest around, just as Drakul wanted. And because it was the White Court that released the information, the surviving Black Court members would be loyal to Drakul, just as he wanted it.
I suspect Mavra either knows this, or suspects it to be true. So she's planning on overthrowing him at the Stars and Stones. It's the real reason she wanted the Book of Kemmler. She's gathering as much information, and power as she can. She's pretending to be loyal to Drakul, for now. When the time is right she wants to replace him.
