"I agree, we deliver Gorlak and the egg to Themberchaud first.  We can fill in the others after that."

Gratefully accepting the flute from Pax, Kaylyn examines it carefully.  She instinctively casts Detect Magic as she does so, just to be sure.  No matter what she then tries a few notes and then some more.  Soon she is lost in a quiet song.  She closes her eyes and lets the music fill her soul and feel it lift her spirits.  That night, as she sleeps, the song fills her dreams.  She walks along a quiet stream, the song of the flute filling her mind.  The Ki-rin is then by her side, encouraging her.  Fear not, the darkness will not overtake you.  This gift of music will help guide you, make you stronger.  What is your name, how do I thank you for these gifts?  As I said, you are mine.  I will show you what you need to do,  Do not let the darkness overshadow the light of your soul.  You are mine, take these gifts and use them well.  The Ki-rin begins to fade and its last words reach into Kaylyn.  Renrin, my name is Renrin...

The following day there is a light in Kaylyn's eyes that Rhyana and Kastix may remember from when they first met her.  She was more herself, lighter and happier than she had been in quite some time.  The darkness of the underdark did not seem so imposing as it had before, at least to her.

"Let's go visit a dragon." she says, a smile on her face.

The next day, Rhayna wakes up with an headache. She dreamed of fungi and spores the previous night, after her watch's shift. There was also a vaguely female form at a distance, she could not see nor tell who that figure was, but she senses it was the Lady. Her head also felt stuffed, like she has been wearing a helmet that she hasn't taken off for a long time.

Then Rhayna sees Kaylyn, and something seems to have changed in her last night. She seemed happier, and there was a light in her eyes. For some reason, it reminded Rhayna of a time that it seems lost to her now. She remembers the town where she met Kaylyn for the first time, but she also remembered the quietness of the libraries of Candlekeep. She was taken back to a more "normal" time, where she didn't have to watch for her life at every moment. And like that, her headache receded, and her head no longer felt stuffed. She was a little more like the old Rhayna.

Here's a fresh map. The group is in the cavern at the top right.

In the morning while everyone is eating breakfast Pax walks up an over to the portal stone. She shrugs and casts comprehend language on herself as a ritual while touching the stone.  Then if that reveals nothing she casts cure light wounds on the stone. 

After the rest, while everyone is milling around cleaning up, preparing to leave, comparing dreams, etc, there is a loud crack from the top of the mesa where the obelisk rests. Looking up, there doesn't appear to be anything or anyone there, but then Sekkar looks around wondering where the human female has got to and asks if anyone saw her wander off. Rhayna says that she thinks she remembered seeing Pax ascend the nearby ramp, and that perhaps she had gone to the obelisk.

Sekkar went to the potential portal to call the always wandering geirl back - after all she was their guide and it was time to go. He looked down in surprise yelling to Rhayna : "Are you sure? There is nobody here."

“I believe she cast a spell while touching the obelisk.” Says Rhayna scratching her head.

"Do you think she was foolish enough to cast magic into the obelisk?   We have no idea what would happen.  She could have been transported anywhere, any plane."

She turns to Gorlak.  If he is conscious; "What does that obelisk do?  Where does it go, that's a portal is it not?"

Gorlak doesn't respond to Kaylyn's question. It could be that he doesn't understand her language, or that he is simply stubborn. Or it could be because he has a gag over his mouth. It's hard to tell...

Kaylyn reaches down and removes the gag from his mouth.

"No tricks, tell us what you know."

After Kaylyn demands answers from the duergar, Rhayan sits close to him and crosses her legs. She brings her pendant and touches Gorlak and casts Zone of Truth centered on him.

Rhayna looks Gorlak in the eyes. “Please, you might not realize, but the whole Underdark is in danger. You may yet help save it.” She studies him, even with the spell, he may not be telling the whole truth. (Insight check on Gorlak: 13)

(Did Kastix hear her casting Cure Wounds since it has a verbal component?)

After everyone wakes up, Kastix will check his pockets, count his coins before turning to others, "When we get back to town, an investment in diamonds about 300gp would most like be of great sercurity for us. If the cost is split among us, it would be affordable and there would be no disagreement if any one of us need it's use,"

(Rhayna is fine splitting the cost for the diamonds.)

(Sekkar would join but he is broke and even indebted to others)

Rhayna checks her funds. “Does 100gp helps?” She asks Kastix.

"Leave it until we get to town," Kastix states waving off the money.

(Zeno will also chip in, and may have some additional funds unaccounted for...not sure what happened with the money from the treasure he sold.  I’ll look into it...)

At first Gorlak simply responds to Rhayna's heartfelt plea with a disdainful tirade in the duergar dialect of Dwarvish: Tha cainnt uachdar coltach ri biastagan neònach. But when Sekkar responds with a Dwarvish insult of his own, Gorlak realises that the language barrier is not an adequate defense. Furthermore, the lizardman is clearly ready to threaten him with Dawnbringer's hateful light, so he relents and answers Kaylyn's questions, still in Dwarvish but with Sekkar translating.

The obelisk's original and true function is unknown to me but it currently serves as a kind of portal. It transports to and from a location less than a mile from the west gate of Gracklstugh.

He appears to be telling the truth.

Seeing Rhayna cast her spell she knew she didn't have much time, but she wants to maximize the questioning and she casts Charm Person on Gorlak (WIS DC 16) "Who are you working for, what is your purpose in working with the demons?  And why is this egg here?"  Kaylyn continues to question him.

Gorlak simply sneers at Kaylyn as she casts her spell at him. She can hardly see his lips moving behind his dark beard, and it is difficult to read the blank white eyes with no pupils, but the string of Dwarvish words that issue from his mouth are clearly insults.

(I forgot to roll the CHA save for Zone of Truth, but I added it on the end of the post in which he replied. He actually passed with a nat20, and according to the spell Rhayna would know that he passed. However based on her Insight check, she believes that he was actually telling the truth regardless of the spell. The way I read the spell, the target has to roll the CHA save every time it starts its round in the Zone, so they can continue to question him for ten minutes, and I suppose I'll just roll the save each time and respond accordingly.)

(No such luck with Charm Person though. A save is a save)