The Goblin Moshcave and... suspicious letter?

Our story begins with an inebriated ranger. In between belches, he did a good job backtracking the (dead) goblins to their lair. Which we found. Defended.
 
Our first attack revealed goblins, a bugbear, and wolves. Oh, and we forgot to rest so our spells were depleted... leading to a long rest and return. We did try to cover our tracks by dragging away corpses and did a pretty good job of it (none seemed discovered when we returned), but to no avail.
 
On our second visit, the lair was awaiting our return had organized a trap at the Moshcave Mouth. We were immediately outnumbered but the warriors created a very successful kill pocket. The goblins were literally mobbing to reach us. So I took advantage of the overcrowding and launched what I though was a waterblast I had picked up. However, as I inhaled for my voluminous incantation, I nearly choked on toxic fumes. I did everything I could to keep my composure, concentration, and sorcery under control, but I can only guess I stepped into the wage of Dagos’ intoxicating breath. In any case, my saltwater blast came out more like an acid bath and, while many of the buggers ducked and gibed, I hit one square in the chest taking it down after a short time. I have now committed that caustic variant to memory (even if I have forgotten the saltwater original!).
 
Unfortunately (for us), some hobgoblin commander (?) showed up to re-organize the goblin mosh troops into a more sensible and effective force. The moshmob turned into more of a security force. And the easy targets disappeared into cave crevices and hideouts. Fortunately, our bard, Barton, stepped deep into danger and pulled a stunning (and deafening) thunderclap out of his arsenal, and the goblins went flying. Barton: 1, goblins: -3. Then (I gather) the hobgoblin commander stepped out of the shadows and took down Barton.
 
Ultimately, we rallied to divide and conquer the lair inhabitants, including the commander. The lair seemed vaguely familiar, almost like I’d been there before. But when we cleared it, we found a merchant prisoner. And a letter which seems to explain the unusual (?) organization of goblins and hobgoblins, not just at the lair but perhaps to explain the suspiciously organized attack on the young Noble, Titus.
 
If we can source the letter, we may very well find who is behind the mortal threat to Titus or, at least, his seat of power.