Mordekai will pass Ulthan's information on to the rest of the group, and then Mordekai will take first watch, and be in contact with Ulthan every 10 minutes or so.  As the end of Mordekai's watch approaches, he'll strongly suggest to Ulthan that he comes in to rest too.  "You'll need to rest too, and there's not much you can do out there by yourself.  They can't get in here, but if you come and knock eighteen times, I'll teleport out and bring you in."

If Ulthan's eighteen knocks happen, Mordekai will use Dimension Door twice - to appear just the other side of the door, and then to bring Ulthan back into a safe point in the library room.  Either way, when his watch ends he'll settle down to get rest.

(I hope that's not taking liberties with the whole Long Rest/taking watch mechanic?  I don't know what the exact rules are, but figured doing it during the first watch takes less liberties than casting a couple of 5th level spells halfway into a long rest!  Mordekai would get those spell slots back after a short rest rather than needing the full long rest for them, but...happy to be overruled on whether or not I can use that to get Ulthan inside...if he even wants to be trapped in here with us!)

The eighteen knocks on the door never come, Mordekai eventually settles in waiting. Eventually though there is a heavy thud on the door. Dust settles from the edges. A very heavy thud again as something large and heavy slams against the door. The door flexes slightly in its frame, the bottom jammed against the edge of the dome, but the top of the door having nothing pressing against it.  Another heavy thud. 

It's been 3 hours, so you sadly haven't achieved a long rest. It sounds as if someone is attempting so pry the door open or smash it down. 

Mordekai will immediately reach for his Tome, hoping the door holds long enough.  He walks out of the Dome on the far side of the door, ready to jump back in if it breaks, and writes to Ulthan, "What's happening out there?  Are you safe?"

Ketch rolls over, pulls his blanket more securely around him, and tries to go back to sleep.

"Here already?" Lionel opened one eye, listened to the banging outside and mumbled the first idea that came to his sleepy brain. "You think we can drop some bookcases on top of the hut to block the door?" If the answer did not come immediately, he closed the eye again and fell back to sleep.

Ulthan responds "hrmpfh some elves bats giants entering pit safe for now hrmpfh"

Meepo grumbles as he gets to his feet. He waits for Mordekai to step back into the hut. "Mordekai need talk elf prisoner." Meepo says, waving in the elf's direction. "Need convince talk those above. Get them leave Meepo friends alone, or Meepo friends summon princess and let free, not fight. If leave Meepo friends alone, Meepo friends rest and fight princess. No choice but chance we win. If no help us then just free princess and be done. Either way princess freed, but, if above people want princess defeated, then only chance help Meepo friends." he glances to the door. "Meepo friends easy free princess before giants inside."

     Ketch grounds and grunts as he gets up from his bedroll.  "Let's just unleash her already," he says with a growl, not really having been able to get back to sleep.  

     Ketch nudged Lionel with his foot.  "Get up, no sleep for the weary!"

     Picking up his shield and axe, Ketch readies himself.  "We release her and cannot make a deal or something and have to fight her, then hopefully we just fight her.  Better than her on one side and an army who hates us behind us.  If we make a deal with her, then maybe we can negotiate with the army as well.  Either way, it's time to just get it done..."

"No." Meepo says flatly. "No open prison until Meepo and Meepo friends ready." he crosses his arms over his small chest and stands firm. "Unless queen no back off, then have no choice, but Meepo hope queen not stupid."

"I'll see what I can do."

Mordekai thinks back to where all the undead and golems had appeared, making a mental note of the furthest room, and will Dimension Door to what he hopes is a hidden corner where nobody will see him appear. Still in full disguise as the elf, he mutters to Quinn, "I'll need your help here!"

He rushes out from around the corner, rubbing his eyes as though the huge bangs on the door had woken him up, "Stop! What are you doing?! They're not here, they fled when I told them you were about to arrive. Teleported out. Don't break that door! We need that in tact to help keep the Princess locked away! They may be back. In fact, I'd bet on it, from my very brief conversation with them. But they can't make any progress if we all just camp out here in wait. Might I suggest, as one who's spoken to them and understood their intentions, that we take this opportunity to rest, take watches in case they return. We have an army, what can they do when they return and we're still here? Even less if we're rested up from the march!"

(Not sure if Mordekai was faced with their leader or not. So depending who he's speaking to, he may be slightly more respectful if someone who's clearly in charge is stood there)

(Roll deception) 

OK... come on random dice roller, don't let me down. 

Deception: 29

Mordekai, wrapped in his illusion, with Quinn along for the ride, vanishes and appears just inside the cave that led to the river. He glances out cautiously and sees a whole array of people down here. In the table room, as well as in the room with the door he sees a few dozen elven soldiers, a few squad mages, and three of the hideous giants. They apparently seem to be fashioning a device that looks like it is intended to pry the door violently out of the frame it's within, the giants waiting while a couple of engineers work on some metal prying bars and a pulley system.  There's a bunch of hammering going on. A woman who looks like a captain or some other military leader stands behind them. Having found his mark, Mordekai takes a moment to take on his role. Quinn vibrates with excitement as he readies to morph Mordekai's voice. 

Mordekai rushes out, trying to look disheveled. "Stop! What are you doing?! They're not here, they fled when I told them you were about to arrive. Teleported out. Don't break that door! We need that in tact to help keep the Princess locked away! They may be back. In fact, I'd bet on it, from my very brief conversation with them. But they can't make any progress if we all just camp out here in wait. Might I suggest, as one who's spoken to them and understood their intentions, that we take this opportunity to rest, take watches in case they return. We have an army, what can they do when they return and we're still here? Even less if we're rested up from the march!"

The audience spins to look at Mordekai and the thrill of the stage of life rushes into Mordekai, giving his every word and motion extra oomph of realism. The Captain glances at him, and also in common says, "What? They had clearly messed with the keys in the lock!  De'thenius said the bindings were broken."  She looks accusingly at one of the squad mages who looks about in a bit of a panic.

He replies, "I...I believed they were. But i did say they 'appear' to be, not that they certainly were. Perhaps they used the key, but then R'osh and his scouts scared them off?"

The Captain looks to Mordekai, "Why did you not return and report? You know what, it does not matter. Staff'althus, stop working on the door, we best leave it intact."  She glances at Mordekai, "Very well, come R'osh, the Raven Queen is above, she will want to hear what you learned from these intruders directly. And you'd better speak Sylvan to her R'osh, you know she hates the common tongue." 

"Get lost, Berth!" Lionel did not even open his eyes to Ketch's "gentle" nudging. The name of his long lost (and avenged!) friend which had a similar habit, would be a hit on the depths of the sleep - when one is completely lost in a happier place. But Ketch could take it as he wanted. Since pounding at the door stopped as well, there were no incentives to wake up anymore. And as a true soldier, Lionel used any free minute to get so much-needed rest.

"Yes, indeed! I am sorry, the journey ahead of the army is often tiring. Forgive me, I took a moment to rest before reporting. I thought I had more time, you made good haste. Oh, I hope she's not too annoyed at my delay in reporting! If you don't hear from me again, you can assume the worst!" With that, Mordekai runs out of the room, towards the stairs, hoping to find a spot where he's alone and out of sight of everyone, where he would be able to teleport back to the group unnoticed (although he doesn't do that just yet). As he goes, he'll mutter to Quinn, "I don't suppose you can translate my voice into Sylvan?"

Ulthan is who knows where, Mordekai has seemingly followed, Lionel refuses to awaken and Meepo refuses to do anything until everyone is ready.  Meanwhile there’s an army on the other side of the doors that has grown suspiciously quiet…  Ketch is thrilled about none of this.  The Half Orc sits on the side of the hut furthest from the doors and stares at them, waiting for them to fall at any moment.  His hands clench and unclench on the handle of his axe and he runs through battle scenarios in his head.  None of them end well…  But he’ll be ready for when they begin at least….

Quinn shakes his head, "No...sorry...I can not translate meaning in the way you desire." 

From behind him, the Captain yells, "What the hell? We go together!"  To the others she turns back, "No one leaves this door for a second for anyone but me or the Raven Queen herself!"  Then she hurries to rush after Mordekai. 

Mordekai runs ahead. The entrance room just inside the stairs is as good a place as any for him to teleport back if he wishes, the Captain is behind him and out of site and there's no one in there.

As the Captian comes around the corner, Mordekai will turn back and use his Fey Presence ability to attempt to charm her (DC18 CHA saving throw).  Then he'll drop to his knees in an apparent show of desperate vulnerability.

"Please, don't make me face the Raven Queen right now.  In truth, she terrifies me.  I practice the Common tongue far more than my Sylvan because that is what my role as a scout requires, and I feel her judgement for that.  And I am just so tired.  I haven't rested properly in days.  There really is little to report.  I interrupted them as they put the keys in the door, so they haven't opened it yet.  I threatened them that our army was a matter of minutes behind me, and they took me captive.  I thought they were going to kill me, but they must have realised what I said was true, and that even if they got rid of me, their only hope was to flee then and there.  They may return, but if they do we are here and waiting.  Oh, I thought I was going to die!  My nerves are on a knife edge, and if I were required to report directly to the Queen herself, if fear I may say something wrong, accentuate my Sylvan with a Common accent, or something - can you imagine her wrath, given the current tensions already?  Please Captain, if you value my services as a scout in any way, pass on my report and recommendations for me, and allow me to get a night's rest, I beg of you."

I'll assume this needs a Persuasion check? (If you'd prefer Deception again, it's the same roll anyway). I'll roll with advantage assuming Fey Presence works, and if not just take the first roll: 26

Charisma Saving throw DC 18 : 5  oops, forgot advantage:  11

The captain at first shows a distinct disdain for his groveling, and her being a fey creature herself seems to resist his influence, but eventually it seems to seep into her thoughts and she softens.  "Fine, fine, stop.  Disgusting. So desperate you'll try to convince me you don't know your native tongue. You're clearly so tired you're delusional.  Just...tell me what you know about them and I'll deliver the report myself. Then you can get out of my hair and get to rest and get your mind right before you report back to me." 

Mordekai provides a brief, but uninformative made up description of an encounter, and then watches as the Captain storms off up the stairs.  Quinn practically shivers with joy after she's gone. "Those lies were MOST satisfying!"

With the deception done, Mordekai can easily return to the book room and the group can get a long rest. Unfortunately Ulthan is not with them, having trapped himself top side, outside the enemy lines.

Mordekai will indeed return.  He'll find a dark corner and Dimension Door back to the group.

"Well, the army is outside.  I assumed the role of the scout here, and think I've persuaded them that we fled, and they're camping out and lying in wait for us outside of the door.  So they hopefully shouldn't bother us while we rest, so long as we're quiet."

He'll also check in with Ulthan once more before returning to his own rest.  "Where are you? Are you safe? We seem to have found some brief peace and quiet.  Keep lying low if you can for now."