Arnuanna
Tiefling man from Leurisan, member of the Tide in Kaarst, and brother of Orianna.
On 12 Thelliea the party found Esker dead in the secret compartment hidden behind the wine racks in Ser Reginald Kobolwitz's wine cellar. In his fist he held a crumpled note.
J,
My informant has confirmed that Kobolwitz did have our quarry in his possession before his demise.
You and E are to enter the manor quietly and secure the blade. It will be well hidden – the old man wouldn’t leave it out in the open. You know what eccentric rich fools are like – look for a hidden safe or vault.
I’m told the manor is locked up and no one has been inside since someone set off a trap while the place was being cleaned. As long as you don’t alert the guards outside, you should have the run of the place.
When quarry is secured, bring it straight back. I’ll be waiting for you in the cask.
A high tide carries opportunity (in elvish)
— V
Because he was holding it, the party assumed the dead man was the addressee referred to as J, and speculated that he had been betrayed by the person referred to as E, who must have taken Ser Kobolwitz's scimitar, and possibly also his necklace.
On the evening of 14 Thelliea, the party met Orianna in The Baron's Cask, who explained that J is her brother Arnuanna, E is Esker, and V is herself. Since Esker is a human man and Arnuanna is a tiefling, it was Orianna's brother who betrayed and killed Esker. She explained that Arnuanna never returned from that mission, prompting the party to suspect he had joined the Knives of Mystra like Uthan had.
In the three days following the party's defeat of the bone devil,
After the party defeated the bone devil, Vichthart made sure to check the defeated Knives of Mystra they'd fought in the cavern beneath Kade Sirrine Kathedrale, but none of them was a tiefling. He also visited Kaarst City Watch Headquarters to check if any of the incarcerated members of the Knives were tieflings, but again none of them was. In the three days that followed, Mira asked Orianna if she'd ever seen the twinned flame symbol before, and she recalled seeing it on a piece of paper that Arnuanna had, which seemed to her to be a letter with a seal. Mira explained that it was the symbol of the assassin faction of the Conflagracy, the ruling power of Dhintay.
On 19 Thelliea, the party met with Galesong Thervan Indále and Sable Warden Meriele Berevan in Kade Sirrine Kathedrale for a final debrief. They went through the salient points of, amongst other things, Irann Rhogar's journal now that they'd had time to investigate it properly. Irann Rhogar had actually written about meeting a tiefling named Arnuanna, who had acted as his liaison with a benefactor and advisor (whose identity Rhogarr hadn't written about). Shortly before his death, Rhogar had written that Arnuanna was planning to leave for Brenhalt.
The party jointly passed this information on to Orianna at The Baron's Cask, who decided that her next destination after escorting Father Traulam Eugen to Senneborn would be Brenhalt to try and locate her brother.