This is a small point, but I find it interesting that the first time Mavra sends one of her minions at Harry, it's when he's in a car; with Thomas, entering the apartment or condo complex where Arturo Genosa is having a party announcing his new movie. After the attack both Thomas and Harry become aware that someone/something else is out there. We can be 100% certain it was Mavra.
So why was Mavra there? I ask this because she had her minion take the place of the security guard before Harry and Thomas drove up. To refresh your memories, the guard wasn't dead, he was having coffee at the front door with a second security guard instead of being at his post. This meant Mavra was already there and saw an opportunity to test/attack Harry when the guard left his usual position. (Unless Mavra has the ability to make long-range mental suggestions to ordinary mortals like; " I should get some coffee now," which I don't remember ever being listed as a power of the Black Court.)
So did Mavra know Harry and Thomas were on their way their way to see Genosa? This would be odd because Harry didn't know he was on his way to Genosa's before Thomas talked him into going to see him. The implications of that are disturbing, to say the least. Was Thomas in league with Mavra, at least to a point? Even if Mavra had one of her minions following Harry and or Thomas all night, and occasionally checking in via long-range mental communication, Mavra was already outside Genosa's. An alternative explanation; which also seems odd but not impossible, is Mavra was scouting Genosa because she wanted to find out how an ordinary mortal was defying or avoiding the control the King of the White Court. Harry's appearance gave her an opportunity to test or attack the wizard. Did she even know Thomas was with Harry? Perhaps not.
There's one other odd moment in BR. During the fight with Mavra's minions, the one ear'd black court vamp says, "Raith's second in command," the vampire rasped. "As well as the White who betrayed us. Now you're both mine." When did Thomas betray them? Bianca betrayed Thomas, so you can hardly blame him for then taking Harry's side. Unless that betrayal didn't happen at Bianca's at all.