It’s a messed-up quest. Below is a little information related to the task of conspiring against you. Regardless of whether you choose Istiana or Arzagos, you will surely encounter the same quest.
This is part of the main storyline. For sure, at the current stage the quest looks raw, because the game is in the early access stage of Steam. In the future everything can change. During the game you will often receive messages that the task has failed, the progress of the target has been achieved or has been reset. So the game shows you the conspiracy, that only increases with the time. On the quest page you can see general information about the conspiracy.
As far as I know, you cannot stop a conspiracy in its infancy form. I’ve tried to track down and kill Istiana, but she’s invulnerable and taking no damage. The only logical alternative is just to wait. As the conspiracy continues to escalate, it will eventually escalate into war. Its size may be different from your social status, your allies, your location, but in my case it will start a war against the Western, Northern and Southern Empires. At that point, the quests will be active.
You will be ordered to either destroy all enemies who have declared war, or find each commander and make a truce with him. The latter, unfortunately, can only be done on the battlefield. The choice is yours, but to make peace is much cheaper and easier. The purpose of this guide is to make you understand that there is no way to stop the conspiracy in its infancy today! That is, the war must still begin.