I think Sertorius's plan The Whole Deal is close enough, but there are a few rough corners that can be smoothed / things that can be added. I may make such a plan soon. Meanwhile, time for observations.
First thing, do not mention the Count or make appeals to authority. That's hiding behind someone's skirts.
We're a foreign witch and this is a public confrontation, if we back down or rely on authority other than our own we risk damaging our standing severely.
Second, while there should be tactical considerations, this works best told as a
story.
Tell the priest of the entire journey, the fight with the Khornate berserkers, of the magnificent stand of the Men-At-Arms, that fought with the Lightfangs side by side, sharing all of our perils, tying down whatever massive enemy forces they could.
Ideally, the listeners should be "there with us": the landing on the docks, with us, the Ulricans and the Dwarves hammering at the Norscan sheildwall; then sending forces to different places in the town to look for the prisoners and prevent the Norscans from mustering an army. Then in the streets: the high priest should briefly hear of how we and the Ulrican contingent routed a force of Khornates with minimal casualties (do not cite the magic-divine duel with the shaman, the Yilvathoi would not understand). Then they should be surprised with us as we spot the ritual on the hill. Do we make it a Chaos Ritual, or a demon-summoning one? Whatever, just do not utter the words
Daemon Prince. Daemon summoning can also happen in a battle, right?
While that is true we are not in Erengrad right now and I don't think the Highest Priest of Ulric in Ostland and a man the Ar-Ulric clearly trust's is someone that would spread around that the goal of the ritual the Wolfs died to help us stop was trying to summon a Daemon Prince. Telling this guy would fall under the whole alert the proper authorities Religious and Secular that the Norscan tribes are conducting rituals at the current time to summon things like Daemon Princes. I thing the High Priest of Ulric in Ostland would find that important information to know and would agree that stopping such a thing had to be done, though the cost was high.
Then, the High Priest of Ulric should be briefly facing the same question: how to stop it? Our answer, that Urskoy was on-board with, was to have the infantry tie up the enemy forces, while
us personally and the Knights of the White Wolf would reach the top of the hill from the side on our steeds.
Point out then that even with those dangers, and that despite that as volunters the White Wolves didn't have to even be on this mission at all, Urskoy insisted that he and his men act as the vanguard, despite the extremely dangerous nature of the role
Then, the doom part: the PlagueWave of Nurgle killed a dozen knights and all the steeds. As the reserve Livgard converged on us, we had to do the same manoeuvre: the remaining knights on foot would fight a holding action, allowing us to break through, to kill the Shamans and free the prisoners that would have otherwise been fuel for the sacrifice.
Then the hill exploded, and we were unconscious, found by our allies.
As overall comment, we can say:
Another argument we can put forward was how the mission was completely out of our expectations in term of danger. I think we started the mission expecting somewhat ordinary Norscans, and we ended up fighting dedicated Chaos sorcerers, their blessed bodyguards and a pissed off Chaos warlord.
Finally, at the
end of the tale, apologise for
one thing: not having looked for the funeral of the Knights and Men-at-arms. And add that after this mission you will look for the last of the knights, and heal him if it is in your power, since you did not known he was crippled.
Why were you not there for the funeral? Because of being too preoccupied with where the enemy will strike next, and also healing our second in command that got nearly ripped in two by the poisoned blade of the Chaos-mutated lord of the Norscans.