Dirty Laundry

 is a faction quest in.

Synopsis
Director Castol told me that a Vailian Trading Company spy in the Luminous Bathhouse sent word about an off-the-books meeting between a Royal Deadfire Company official named Quarno and a Príncipi captain by the name of Töla.

Castol wants me to uncover the details of their smuggling arrangement.

Walkthrough

 * This quest will begin upon completion of Terms of Trade. Director Castol explains the importance of luminous adra to the VTC. If you already completed A Glimpse Beyond, you will receive both Minor and Moderate Positive reputation with the VTC.
 * Head over to the Luminous Bathhouse and talk to Brizze on the upper floor. She will reveal that an RDC operative, Quarno, and a Principi agent, Töla, have bought out the entire first floor and got rid of accidental witnesses - except for attendants - to ensure privacy and confidentiality of their talks.
 * Brizze will reveal her plan too: She will disguise you as a bathhouse attendant to serve the two and perhaps discover the details of their special arrangement. Once you give her the go-ahead, you will dress as a bath attendant and be sent to figure out what's going on. Brizze will provide you with 2 bottles of Rice Wine to get Töla talking.
 * Note that you will be unable to take your *currently equipped* gear, but you will still have full access to the rest of your inventory. Brizze will tell you that if at any time things should get out of hand, there will be a stash of weapons in one of the changing booths (consisting of a bunch of Daggers, Wands, and a Battle-worn Grimoire.)
 * Note that this quest will automatically force you to rest, discarding any rested bonuses (such as the Adratic Glow from using the bathhouse). This happens when you change into the bathhouse attire and back, once when you give Brizze the OK, and another time upon leaving the bathhouse. There is no way to avoid this, except by skipping the quest.
 * Gain information peacefully
 * Töla will be alone at first and you can give her the Rice Wine. If have reputation 2 or more with the Príncipi, she seems to think you look familiar. You will have the option to press her with Diplomacy 8 and Bluff 7. Then feed her another rice wine bottle and you'll be able to learn that not only did Quarno sell her cannons, he also hired her to raid a VTC luminous adra convoy.
 * You can also talk to Quarno and insist on speaking with him. With Diplomacy 8, Bluff 10, or Intimidate 12, you can squeeze him for information.
 * Make sure to steal Quarno's Ledger from the Accountant, who spends most of the time with his back turned, occupied with the aquarium at the end of the left side of the bathhouse. Inspect the ledger in your inventory once you have it.
 * Once you've got everything you can, head back to Director Castol to finish the quest, giving him the three pieces of information you retrieved.
 * Kill the agents
 * You can attack Töla and Quarno at any time while in the bathhouse. Doing so will cause the armed Rauataian Guards and Príncipi Wizards to attack. The fight is very easy, even without weapons or armor equipped. Grab Quarno's Ledger from the Accountant once all is done.
 * Though this route doesn't directly get you any information from the agents (unless you talked to them prior), the possession of the ledger makes up for it (though you won't actually be able to hand it in). Return to Director Castol, who is glad to see an end to the matter, regardless of the methods used.

Behind the scenes

 * In the boiler room you can loot A Pinch of Refined Luminous Adra, which based on the description would have provided an means of increasing the heat and duration of the boiler, or perhaps the potency of the bathhouse waters if one were to mix it with the gunpowder supposedly given to you by Brizze. This is likely a cut quest route.