Since most of you guys are probably nor familiar with muh TES lore (although, let's be honest, everyone still played Skyrim, with or without tasteful rape mods) I will do my best to explain the significance of some of these items and we can hopefully brainstorm some sort of next move from there.
Depending on the thickness of the cloth, the dagger's sharpness might be very impressive indeed. Since this is a setting which allows for magic in rare cases, perhaps the opening in the hilt is for a soul stone, removed during storage for the same reason one would remove non-rechargeable batteries from an electronic device.
Nightshade, of which there are four dried stalks in this folder, is pretty peculiar. Poisons can be derived from it, thus it is associated with assassins and, specifically, the Dark Brotherhood. If I remember correctly, it is also used for the ritual of Black Sacrament.
What's a Dark Brotherhood? It is a cult of assassins that, besides taking money for its contracts, kills to appease its patron deity, Sithis, who is basically the representation of enthropy and misanthropy. He supposedly impregnated some bitch and we call her the Night Mother now.
What's a Black Sacrament? It is a ritual involving a prayer to the Night Mother in order to summon a member of the Dark Brotherhood (one of her "children") and hopefully initiate a contract for someone's death.
The first letter is a report or maybe a letter penned by some constable or minor lord. It could be quite old. It describes who I can only guess is an ex-assassin from the Dark Brotherhood and his encounter with the writer of the letter. I assume that "I'm a loose end, yes, but you will tie me off" is an indirect plea for death, as people who desert from the Dark Brotherhood are inevitably slain by other members for being loose ends. Of course, the lord's involvement with the ex-assassin means that he, too, is going to get fucked. The reference to the "father" is a reference to Sithis, for the Dark Bros believe Sithis to be their father just as Night Mother is supposedly their mother. Metaphysically speaking. Maybe.
Second letter is obviously a copy of an original, meaning that Amaund Motierre is keeping incriminating documents on, in this case, the Domitian. Could it be the same Domitian that sits on the Council and marshal's the Empire's legions? Probably, because we know he is up to no good. His secret plan to bolster a legion in the heart of Cyrodil always smelt like a coup d'etat in the making to me. We don't know any Quintus, though, although Domitian did mention a Legate QuintIUS recently, though these are slightly different names, not to mention common and it could be a coincidence. As to who was responsible for the tracery, it could very well have been Runa, which would make her Motierre's agent. Then again, that's just the only woman we can think of at the very moment.
The second letter is obviously written in code. It seems to speak of something that had been botched but the Domitian is sure that he can make it work with proper assets. The food metaphor makes me think of a poisoning, but it could be any kind of plan. An assassination, perhaps? Not good.
Finally, the third letter is a prayer to the Night Mother, seemingly the same one that would be used to perform the Black Sacrament:
"thus a sonn to his mothr a dottr to thi un hwo unto her gaev birth thus thi faithful rendr homaege for baptism of sins und hoep of deth do we raes our prayr thus thi blest rite nocturn" blah blah, we love killing dudes, lets pray about killing dudes, blah blah, also the night mother is our actual mother or whatever
"of thi unworthsome fashion an ymnaege with skul und rib und heart of mann about thi ymnaege let thaer twinkl candls dimm" refers to the way the Black Sacrament is arranged, with a human effigy made up of human heart and bones surrounded by a circle of candles.
"with a knief of steel let it nott be of iorn but let it be ensacrated by dolors leaf piers the heart of mann agen piers agen und agen piers the heart und whispr such prayr" you perform the black sacrament by piercing the heart with a steel dagger sanctified by "dolors leaf," nightshade perhaps? Maybe the steel dagger and the nightshade enclosed in the folder were both used during the ritual of black sacrament.
"mothr sweet sweet mothr mine send sweet sonn of thine unworthsome sinnr bles with fear und bles with blood" asks the Night Mother to send one of the assassins, her "children," to the speaker to shed some blood, basically.
"dreead fathr" once again refers to Sithis.
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So, the way I see it, the first and third letters, as well as the nightshade and steel blade, seem to suggest that Amaund performed the Black Sacrament. If these documents belonged to anyone else, he could have had them traced like he did with the Domitian's letter, not taken and kept with him.
The second letter suggests that the Domitian is up to no good, and that AM has been spying on him.
The way I see it, we need to act immediately. AM knows his murderbox had been stolen. Imagine the urgency with which he will act from now on.
So, first of all,
entrust the matter to the Penitus Oculatus. Hand over all evidence to them but
keep the dagger in case we need to blackmail AM directly (which we really don't want to do if he can call the Dark Bros on us.) We are one man, they have an intelligence network which spans the Empire. Suggest to Maro that they try to find the village from the first letter by cross-referencing records. I'm sure murders and imprisonments in the civilized provinces are documented, and if not we will know that this occurred in a not-so-civilized province. Perhaps we might be able to find out the cause for AM's black sacrament by following the trail of these loose ends.
Also,
let the Occulati take the boy's body back for examination. Perhaps our attempted poisoning might be connected to the AM/Domitian investigation and we kill two birds with one stone.
Meanwhile,
talk to the Emperor but do not tell him of the conclusions we have drawn or emphasize either the Domitian or the AM as a threat. We could spook the old man into doing something stupid. Maro will probably filter any specifics he deems important anyway. Instead, take advantage of our relationship, built on
honesty and trust, and ask him
"What do you think of Amaund Motierre, truly?"
and
"Why did you appoint Domitian as marshal?"
We need to know the Emperor's history with both people if we are to draw more conclusions.
Since we are mostly relegating tasks, we should concentrate on 1(d) and solve the counterfeit mystery for Vittelius in our own free time. We already set this thing up, might as well go through with it while we have the chance, or else we risk wasting all the time we spent on the matter so far.
MercantileInterest feel free to tell me if this is too broad in scope, so that I can trim this plan down to size.