Many other province lords and other nobles were worth enough to have a personal army, be it a regular one, conscripted in a rush, or hired from mercenaries, were sharpening their fangs too.
The news that Farini has some method to cure the plagues that still ravaged the Naregan Kingdom spread to these people.
Until now, the nobles and the High King were more focused on protecting themselves and their lands from the illnesses. The evolving insects were also a problem, because they spread pathogens and killed plants in orchards.
Now, these people all had eyes on the prize, and this prize was Farini's head. And the High King immediately united many of these noble houses, promising to share the cure with them over missives carried with tamed dragons and secretive horseback messengers.
The Agents I had in his palace told me as much.
And they used these messages to travel to these nobles and influence them.