She can pop past if it looks like they're moving, that's usually good enough to fool vermin.

Easily enough - she can do the same for the sleeping pair of monitor lizards and the next group of spiders too, at which point she hears voices, arguing, up ahead. She's concealed from them by a rock outcropping but she can see the ruins of a tiled floor and crumbling pillars from here.

Okay, two approaches here: mask on, which lets her use it to check alignment, or mask off, which makes her less terrifying.

...They're arguing. It might turn into a fight. Mask on.

She'll round the corner in her bright-shining silvery skull-and-bones horrorshow armor.

"I know it's here somewhere. It has to be. We've got to keep looking." 

The speaker looks like the result of a mad vivisectionist stitching together lizard and man. Green scales surround a yellow eye across half a face and continue on down below the rags he wears, while a single horn curls back from his forehead. He carries a longbow and quiver full of arrows on his back, and is kneeling on a pile of debris and yanking on a particularly large chunk. 

He looks up and notices Estel and freezes.

"Wenduag!"

Standing up from where she was slumped against the wall, bored and annoyed with Lann's idiocy.

"What, did you find it?" 

When she too spots Estel she drops down into a fighting stance, pulling out her own and an arrow. She looks like a cross between a cat and a spider, many-jointed legs curling up over her shoulders through holes in her cloak. She has matching yellow eyes and blue skin and bares her teeth at Estel's mask.

They're clearly allied. Well, sometimes you guess wrong.

She reaches up and removes her mask, and attempts to smile.

"Peace. I thought I was walking into a fight for a minute, but I don't want to start one. I just fell down here from the surface."

"Wait, do you know what's going on up there? There've been collapses all over the tunnels."

"Deskari showed up and smashed a line down the middle of the city with Riftcarver. The city's in bad shape; the dragon protector is dead, too. I can get back up, but I was looking for people who survived the fall first... Which I assume you aren't?"

"No, we live down here. If - damn, if things are as bad as you say, we all have to hurry." 

"The surface isn't our problem, Lann. Did you come down through the Shield Maze? It's back the way you came, made of brick and full of cultists and some dead neathers?"

"They're not dead yet, Wenduag. I can feel it."

He turns to Estel too, "We do have to hurry though, some kids went in there when the shaking started and they need someone to help them."

"No," she says to Wenduag, "I fell. You can go almost see the sky now, if you like, it's just back that way. Why did kids go in, if it's so dangerous?"

"All the legends say that when the need is most dire, the underground crusaders will return to the surface and win back their honor in glory. They thought the collapse would let them make it through like in the stories."

"Ah. Kids of warriors trying to prove themselves with unwise bravery, right." Ata's tribe mostly doesn't have kids but there are enough that Estel's seen this in the last few months.

"Sure, I'll help get them out. And if you want to return to the surface for honor and glory... Pretty sure they'd welcome the help just about now."

"That's terrific! We'll come with you! We just need to find the sword first. Oh - this hall is where we keep the relics of the first crusaders, and one of them is a holy sword, and if we can find it we can convince Chief Sull to bring the whole tribe with us." He says with utter confidence that it will be just that straightforward.

"Even if you find it, Lann, you won't be able to pick it up. It's an angel sword and we're cursed" she spits out.

"Even if it burns me, I'll tie it to my hands if I have to. We have to do something! If we can get everyone, the Shield Maze won't be able to stop us."

Wenduag scoffs at that, and Lann goes back to digging.

"You're still here, aren't you? You must think there's a chance."

"No one's so cursed by their birth that Good won't recognize them if they see it."

Or at least, so Corl keeps telling her, and she's guessing it won't hurt to say even if she doesn't quite believe it.

"You're sure the sword's that important?" Detect magic, on general principles.

1st round: yep, there's magic afoot

2nd round: there is one magic aura and it is Strong

3rd round: it's in a pile of rocks closer to you than Lann, and it has a powerful abjuration and evocation aura, and (36 spellcraft!) it burns and blinds demons who touch it, and it deals holy damage and is incredibly well made, and, unfortunately, it's very broken.

"Ah, I see it," she says, and gets in to lift the rocks out of the way, "Looks like the years haven't been kind to it, but it's still working."

The moment she reveals it Light pierces through the darkness. Glowing warmth rushes over her and her chest bleeds again, painlessly, as a vision unfolds in her mind. 

She is the angel Lariel, betrayed and dying here in the dark. Beside her is a wounded girl, paying dearly for refusing to join the traitors. Those are up ahead, hiding but not well enough, waiting for her to die from her wounds and the poison. It sears through her blood and she knows her time is ending. She can spend the last of her strength on saving the life of her comrade, or on striking back at the traitors.

The greatest threats refuse to hide, the Pike says. Technically, that doesn't apply here. But when you put her in pain with a blade in her hand and monsters to hunt...

"I'm sorry," she murmurs to the girl, and charges.

They scatter and scramble away. A young half-elf with his hair up in a knot shouts back "You and your goddess have given us nothing, Lariel, Nothing! But Lord Deskari will give us everything! And there is no power in the world that will stop His advance!"

The darkness ahead stirs in a wave of horrible piercing chirruping and rustling. The cultists fall to their knees screaming and chanting and the fallen girl thrashes and dies behind her. A nightmare made flesh pours over her and drags her to the ground. 

In her final moments, Lariel-Estel's thoughts are suddenly clear. She sees her enemy and will never bow before him. Her sword flares to life, bright and pure, flickering with rainbow-hued sparks as if it was a sunbeam wrapped in stained glass. The blade slices through the demon's flesh and it recoils howling. With a last burst of strength, she plunges the sword into the rock.

The vision disappears, vanishing in a burst of colors. The heat blazing in her chest fades away and the edges of her scarlet wound close, leaving not even a scar behind. Looking down, she sees the flaming sword in her hand - or, rather, its outline, which lets out another surge of soothing light and vanishes, drawn into Estel's hand. She senses she can bring it back - all she must do is call it. 

"I won't," she mutters to herself; "We won't. To the end."

It's not that she's forgotten she's not alone, but it's not terribly salient at the moment.