Alex Verus has a problem. Not only is his former Master back from where ever he'd vanished off to, but most of Light society seems to think he's still appretinced to Richard.
As part of image rehab, Alex contacts his sort of friend, the Keeper Caldera, to see about becoming an auxiliary keeper. Which is great, until he winds up getting attacked by a mute air mage assassin on the outskirts of London while investigating some kind of disturbance.
As he digs deeper into the case (as well as learning that the Keepers are less like pulp novels and more "Well, that's done, what's the next case?"), he gets caught in bigger webs of Magical politics involving the unbending Levistus on the Light side and the machinations of Richard on the Dark side.
In the center, with a loose data focus, is an independent organization, White Rose. White Rose, while run by Dark mages, caters to all factions of mage society, as long as they're willing to pay. Services include prostitution as well as things straight out of Hostel. Given the organization's access to conditioning techniques, you can sort of imagine what's involved here.
The conflict comes in that a few factions of the Light mage Council don't want the records revealled, lest their lily white image be tarnished. Dark mages, on the other hand, are using it as leverage to gain a seat on the Council.
It's quite ugly, and the Byzantine politics of the situation make it seem like a spy novel on speed in places.
Unrelated to the main plot line, Luna has a new trainer, who happens to be a Dark mage. While we meet her only briefly, it would seem that she will play a larger role in the ongoing metaplot.