Belmarniss can now sorta muddle along in the local common thanks to aggressive use of comprehend languages to hand-translate books after roping a local into teaching her the alphabet. Also she hates teleport traps with every fiber of her being. Also she has figured out at this point that she somehow leveled in sorcerer instead of wizard during the business with the pirates and has no idea why that happened or whether it will happen again. And she has sold this stupid arrowhead to two different curio shops and given up as it seems to be cursed. And she just needs to keep doing what she does, she guesses, till she can teleport herself home. The Yawning Portal is a nicely ironic name.
Alan feels conflicted about being a blackguard. On the one hand, it's against everything Drogan taught him, and he feels bad for betraying his teacher (in a way; it's all in the service of stopping the bastards who almost killed him, right?). On the other hand, it feels right. He's powerful, as powerful as he ever was when he was a paladin, and there's no stupid unintuitive rules getting in his way. He can crush his enemies just as efficiently as before (the kobolds aren't subject to Smite Good, but they mostly weren't subject to Smite Evil either). He feels right, for the first time in his life, and it's all because he did the wrong thing.
He encounters a lone kobold on the road. The kobold is frightened of him, but forces itself to speak to him anyway. Introduces itself as Deekin, says it took one of the artifacts from Drogan's home. He asks why he shouldn't kill it now. Deekin says, reasonably, that if he kills it he'll never find the artifact, because it hid the artifact in a place no one else knows about. In exchange for the artifact, Deekin says he must talk to its master, the great white dragon Tymofarrar, and convince him to free the kobold from his service, and forgive it for breaking the artifact. Alan accepts this offer with bad grace, and heads off to visit the dragon's lair.
In the upper reaches of the dragon's lair, he finds a tribe of kobolds. They attack him, fearing the strange human, and he slaughters them to the last hatchling and continues deeper into the mountain, where he finds the dragon Tymofarrar. Tymofarrar, feeling generous, explains that the attack wasn't originally his idea, and that in fact it was orchestrated by the Fey'ri sorceress J'Nah. Alan requests that Tymofarrar release Deekin from his service, and Tymofarrar makes a request of him in turn: kill J'Nah, and the dragon will grant Alan a boon.
Nathyrra considerately waits until everybody is awake before appearing out of the shadows.
"Hi!" Deekin says brightly.
"Hello again," Nathyrra says. "I have some good news."
"You remember the army of drow guarding Halaster? Apparently they brought artillery emplacements."
"This doesn't sound like good news yet," Garrus says.
"The artillery emplacements have three hundred and sixty degrees of rotation, and could be pointed at their war camp."
"There we go," Garrus says happily.
Snort. "How many artillery emplacements, how are they guarded, what are the numbers like, all that good stuff -"
"There are two, placed atop a ledge to the north of the camp with a bottleneck ramp up to it. The bottleneck is guarded, but I found yet another of those secret passages that leads right onto the plateau; its entrance is also guarded but less heavily, and if we can take those guards down fast enough they won't know we're coming. There are about fifty drow in the camp, most of them low-level crossbow- or swordswomen but with more than a few mid-level wizards and clerics, and about a dozen duergar mercenaries. You can probably see why I don't relish the thought of a head-on fight."
"Conveniently, though, the artillery emplacements are very effective. They accept an offensive spell of up to sixth level from a caster and Maximize it. They can only be used once per minute each, but a maximized Chain Lightning, applied appropriately, could take out about a third of the enemy forces. Combine the artillery with the bottleneck up to the ledge and the ample cover up there, and the enemy’s advantage starts to look slim.”
“I do.”
“What? I thought you were a rogue.”
Nathyrra smiles. “That’s not entirely a misconception, but it’s dangerous to make assumptions in the Underdark - even relatively grounded ones. I am trained in the arts of stealth, yes, but my primary calling is as a wizard.”
"Essentially: we assault the tunnel entrance, allowing no one to escape. We take the plateau from the two gunners on duty - they're high-level, but they are wizards without significant support and we will have the element of surprise, so the party should be able to take them. You and I use the artillery to take out as many of the clustered drow as possible, ideally centering the effect on their captains. From there, we defend the plateau, and when the artillery recharges, we use it again to take out the remaining soldiers."
"Good. We're currently entering the period when the most of them sleep, which is why I revealed myself now; if we assault the tunnel entrance within the next few minutes, we can take the plateau during their off-hours and have that advantage on top of our plan."
"Wow, okay, I guess I'm prepped for it as I get but I wish I'd known last night this was happening on this time scale."
"I'm sorry. We don't strictly have to do it now, but I worry about excessive delay."
"Yeah I can cope just notes for, uh, any future occasions when you enlist a party of adventurers to help you attack a small army."
"A situation I certainly hope won't come up again, yes. At least not under this kind of time pressure."
Nathyrra leads them to the entrance to the tunnel. As she said, it's guarded; two swordswomen appear to be playing a sign-language-based word association game. Nathyrra twists a ring on her finger to turn invisible; after about twenty seconds one of the guards collapses like a ragdoll, and Nathyrra reappears only to immediately cut the other's throat. Then she bends down and cuts the first one's throat too.
She beckons the party onward.
At the end of the tunnel, there's a large rock. Nathyrra whispers, "There will be two wizards. I can kill one of them. Garrus, can you take the second?"
"Ideally we'll be able to take the artillery emplacements before anyone notices we're here - except the wizards, of course, but they shouldn't live long enough to raise the alarm. Then we can cast our short-term beneficial spells before the first strike, and defend the plateau until the emplacements recharge. Any questions?"
"Yes."
Nathyrra casts Heroism for Garrus and Jojo both, and Magic Circle against Evil for Deekin.