Count Hengst von Blitzengaard delivers the news that Prince Aaronev Wilhelm Sturmvoraus has died in "a tragic lab accident" to Klaus Wulfenbach.
Klaus immediately and correctly infers that it was no accident (in fact, Anevka killed him) and that it is evidence that Agatha is in Sturmhalten.
Later, he reappears to protest the invasion, which gives Klaus the opportunity to demonstrate to Bangladesh DuPree the ability of the wasp eaters to detect revenants, an important feature as these servants of the Other can look perfectly normal, contrary to the common (and, in particular, Bang's) understanding that all revenants are of the shambler type.
It may be noted that this is the first von Blitzengaard to enter our story; it turn out to be the name of more important characters (Martellus, Xerxsephnia) as well.