I think this may be my least favorite part of the adventure so far. I was quite looking forward to a social/skill adventure, but this is sort of a mess.
For reference, my players were:
An Elf Bard
A Half-Elf Rogue, multiclassed Bard
An Elf Cleric of Cayden Cailean, multiclassed Fighter (this character had the highest Stealth and Deception scores)
First off, my players didn't bite on the "K" lead, cutting out a lot of adventure content, since it's focused heavily on laying red herrings for "K" and assuming that the players are investigating this.
My players spent the 3 days leading up to the gala laying their own plans, rather than investigating. The Bard succeeded in gathering information about the gala, but no-one asked about Necerion, "K", or the Kelpie's Wrath.
The Rogue initially tried to find information on the guards in the fortress, but since the adventure doesn't mention this being relevant at all, it was pretty much fruitless.
Two of the party members (the Bard and Rogue) decided to put on a performance, with the Rogue disguised as Necerion going around ruining all of the pirates' fun, and the Bard heroically stopping the villain. A critical success on the part of our "hero" made him an instant celebrity.
The Cleric decided to steal the flag from the Blackguard's Revenge, which Besmara cursed her for, and spread a rumor that bringing the flag to the Kelpie's Wrath on the night of the gala would grant a blessing from Besmara. (To make a distraction.)
At the gala, my players were initially interested in Kadhibat, since he had gathered a crowd, but quickly decided that there was nothing to be gained by talking to him, since they didn't really care who "K" was.
Necerion was in disguise, since he had been publicly embarrassed by the party impersonating him, recognized his rival, tipped off Kasbeel, and snuck off without the party beating his Disguise roll.
The Rogue cast Detect Magic early on and then spent most of the rest of the session complaining about the Faerie Fire effect.
The Bard brought a gift to Whark, but didn't talk to her any further, since it seemed an inopportune time. Nobody seemed to think of warning her that The Last Theorem was going to be stolen.
After Necerion pointed out the party, Kasbeel talked to the Rogue, dropping hints that Necerion had seen them, and inviting them to join her in the next procession. None of the characters were suicidal enough to enter an infernal pact with a contract devil. (The Bard did go "Oh! This is 'K'!" after the contract devil introduced herself, though.)
The party decided to stick around for the procession, to see what was up, and the Cleric and Bard used the distraction to enter the kitchens. The PCs discovered that the kitchens and servants' quarters are not part of the gala, and spells can be cast in this area.
Nothing much happened after this, since there are only 3 NPCs in the entire gala.
The party waited for the next procession, and started their fabricated distraction, shooting the flag of the Blackguard's Revenge into the cliff above the fortress with a Beacon Arrow. They buffed up in the kitchen, including the Bard dispelling the Faerie Fire, then snuck into Whark's room, disabled the trap, and found the secret door.
The portal trap in the next room confused the players, and the Rogue complained about the DC of the Arcana check to figure out the trap. They tried each door once and then pretty much gave up on it. The Cleric used Stone Tell to get the answer.
Necerion got noticed by the Rogue's Sense the Unseen shortly after this, and then got absolutely rolled by the party. He just didn't have the action economy to compete.
We stopped here after a 4-hour session. The party is about to enter the mirror room.
Overall, I'm a bit confused by the scenario. It's supposed to be a social/skill scenario, but the gala seems to be nothing more than a short setup for the dungeon crawl, and there are only 3 NPCs to interact with. There's not any meaningful interaction with the gala, and not enough for me to extrapolate off of to deal with the PC's doing something creative. The skill DC's in this chapter were outrageous, and even the PCs optimized for skill use were consistently failing them. I'm sure you'll hear a bit from the Rogue's player on the Faerie Fire curse, but I'm inclined to go easier on that part (this is a fairly high-magic setting, the PCs were warned not to use magic, and there is a place to safely cast spells).