Online:Deepening Shadows

Quick Walkthrough
# Talk to Provost Varuni Arvel in the Sotha Loqutorium.
# Search Chancellor Gascone's rectory.
# Return to Varuni.
# Talk to Luciana Pullo.
# Talk to Artificer Dalomar in Slag Town.
# Follow Gascone's trail with Snuffler.
# Talk to Rarlmir.
# Follow Gascone's trail.
# Investigate the Ventral Terminus.
# Locate Chancellor Gascone Dusant.
# Return to Varuni.

Detailed Walkthrough
Continue your conversation with Provost Varuni Arvel from the previous quest to receive this one. She will tell you to check Gascone's rectory as a place to start the search for the Chancellor. Head on over to Chancellor Gastone's private dwellings within the Basilica. When you enter the room, you'll be greeted by a mess: the room is littered with black feathers, there are documents and books scattered all over the floor, and a pale humanoid creature is skulking at the far end of the room.
:Shrike Talon: "Where did you hide it, you worm...?"
Defeat the Shrike and read Gascone's latest memorandum. Return to Provost Varuni Arvel with your findings. You tell her about the Daedra and show her the note he left. She expresses bewilderment at the presence of a Daedric creature, wondering how in the world it could have breached the celestiodrome's security measures. She'll send you off to find Proctor Luciana Pullo. Do as she says. When you find the Proctor,  she'll be just outside the Basilica, dispersing a panicked crowd.

:Proctor Luciana Pullo: ''"I'm not here to speculate on Lord Seht's whereabouts. I'm here to clear the square."
:Citizen: "You don't know do you? I knew it. This is a disaster!"
:Proctor Luciana Pullo: "If you want to panic, do so in your own homes- not in the pubic square. Now disperse, or be dispersed."
:Proctor Luciana Pullo: "Get them moving."
:Clockwork Enforcer: "You heard the Proctor. Return to your homes."''

You ask her if she can spare any bodies for a city-wide search, to which she replies with a definite "no." Her resources are spread thin as it is. She does, however, direct you to an interesting character, an artificer, by the name of Dalomar. Find and speak with him, and see if he can assist you in locating Chancellor Gascone Dusant.

Tracking Gascone
Go find Dalomar in Slag Town. He's the Dunmer with the looking device over his left eye. Speak with Artificer Dalomar. Right off the bat, he tries to offer surgery to give you clockwork augmentations.
:''"Well, well... look at you, full of fleshy-bits. Not a scrap of brass on you, is there? That won't do! That will not do!
:''I can fix you up. No bother at all! Maybe new feet. You need new feet, don't you?"
:No thanks. I need to track a missing person. Luciana said you might have something that can help.
:"A missing person? How mysterious! You wouldn't be looking for Sotha Sil would you? I hear rumors, you know? All kinds of rumors. Something about him turning into a crow? Or was it a frog? Never mind.
:Luciana did you a favor. I have just the thing!"
:Good. Can I see it?
Dalomar walks over to a Nix-hound Fabricant. A sprightly creature, it leaps into action.
:Artificer Dalomar: "Woah! Cool those cogs, you twitchy rascal!"
:Artificer Dalomar: "This little scrapheap should do the trick.... Meet Snuffler, the tracking Nix."

Say hello to Snuffler and let him sniff the Note Gascone left behind.
:Snuffler: " "
With the note Sniffed, follow Snuffler, who is off the moment you let him go. Chase Snuffler to the big door that leads outside the Brass Fortress. Follow him down the path to the right of the door that leads to the bottom of the oily canyon, and pursue him west. The first thing you'll encounter on your lovely jaunt through the Radius is a pair of Nords... one of whom remains asleep, even as you step on him. Talk to this Rarlmir character and see if he can tell you anything about Gascone's whereabouts. Maybe he's seen Gascone recently. Besides, it looks like Snuffler's lost his scent, seeing as how the little rascal has stopped by these fellows.
:''"What are you doing nosing around here with that ugly beast? Joneif and I haven't done nothing!"
:I'm looking for Chancellor Gascone. Have you seen him?
:"Chancellor who?
:Oh, you mean that brass-arsed fancy-boots that came running through here? Yeah, I seen him. Dragging his silly apostle skirts behind him like a broken wheel-chain. Seemed like he was in a hurry. Pretty suspicious if you ask me."
:'''My fabricant's lost the scent. Which way did he go?
:"Yeah, the grease mucks up fabricant snoots. That's why we're down here. Would't want the constables to see.... Never mind!
:''Your man headed west. Should be some oily footprints about. Follow those tracks and you'll find your fancy-boots."''

Just as Rarlmir said, there's a trail of oily footprints on the ground, presumably left by Gascone as he hurriedly fled from the Brass Fortress, stepping in the oil lining the ravine and tracking it everywhere. Follow the oily tracks and eventually, you'll come across a strange note. Upon reading, it looks like Gascone's been targeted for assassination. He's apparently betrayed someone, and whoever wrote the note keeps referencing shadows in their words. There are also dead assassins in dark armor scattered around near the note and down the path.  Continue following the oil prints. Some way down the line, a pair of Daedra will manifest: a Shrike Crowcaller and a Shrike Shroudweaver.
:Shrike Crowcaller: ''"The traitor can't be far. Find him!"''
Defeat the Daedra and continue searching for Gaston. Not far from the site of the Shrikes' appearance is a wounded cultist. Speak with her, and see if she can tell you anything about Gascone's whereabouts. She keeps mentioning a night mistress, and reveals that Gascone gravely wounded her before heading off to the Ventral Terminus. If you speak with her further, she will reveal that Gascone made a covenant with Clavicus Vile who made a deal with her mistress, and that Gascone apparently broke the part of the deal with her mistress by losing an artifact that she wants. She tells you that there are Skaafin around the Terminus protecting Gascone, and insists that you leave her be. Leave the cultist to her death in peace and pursue Gascone west, towards the Ventral Terminus. There are swaths of Skaafin lingering outside the location, purportedly protecting Gascone. Cut them down and get Snuffler to investigate the things Gascone has left behind in the canyon. There's a bag of Uneaten Rations, a Bloody Bandage and a Strip of Apostle Robe for Snuffler to sniff. With the Nix back on his trail, follow Snuffler to the entrance to the Ventral Terminus. Suddenly, you'll hear a voice over an intercom. It's Gascone!
:Ventral Audiometer: ''"What? Who's out there?"
Approach the device and speak to the Chancellor through it.
:"Begone, whoever you are! I sealed the door, and it shall remain sealed for as long as necessary!"
:Chancellor Gascone? Varuni sent me to find you. We have some questions.
:"Questions? You think I'm foolish enough to let you in? No, this door will remain closed. I just need time to work this out- to smooth things over. Simple. Now, leave me be!"
:What have you done? Did you make a deal with these shadow cultists?
:"Who I keep council with is none of your concern!
:''You're just like Varuni. So uptight. So naive! If you value your life, you'll leave this place. Now."''
Since the door to the main entrance is shut tight, you'll need to find another way in. Look to your right- there's a hill there. Climb the hill, cross the bridge at the top of the hill, and turn right towards the Ventral Terminus. On a small cliff above where you were talking to Gascone, there's a smaller door that leads inside the Terminus. You might have to fight a few fabricants and Skaafin on your way up there. Open the door and enter the Ventral Terminus.

The Ventral Terminus
:Chancellor Gascone: ''"So, you found a way in after all. Impressive. Too bad it's a dead end. Unless you can smash through solid bedrock, you'll never find me."''
While investigating the Ventral Terminus you will come across find a massive clockwork automaton: the Imperfect. It looks a little out of order. A nearby manual will tell you all that you need to know about activating the factotum. There is a puzzle with 5 valves and a valve reset station. Your goal is to direct the steam towards Imperfect to charge the animo core next to it. Start with the valve closest to the reset station. Each time you activate a valve the direction of the steam changes. You may have to use a valve more than once to get the steam in the right direction. The first valve needs to be turned once, the second one twice, the third one needs two turns, the fourth one needs turned once, and the fifth and final valve needs to be turned once as well.

With the animo core filled, use it to power the Imperfect. You'll need to activate the Imperfect in order to make further progress. It will smash through the walls that are blocking your way. Soon enough, the Imperfect will lose power. Head to your left and climb up to the second floor to find a new charged animo core. There's one sitting at the end of the hall next to a few factotum charging stations. Refill the Imperfect's animo core slot and continue on. You can either sit back and allow the Imperfect to fight the Skaafin Gascone summons to protect himself, or you can assist the machine. Just make sure to stay out of the way when it swings its arms in front of it and smacks the Skaafin down, and don't get in the way of its lasers. When you get far enough, Gascone will reroute an energy gate right on top of the Imperfect, destroying the factotum. With the gate's beams rerouted, you can enter the portion of the Terminus the gate once blocked, to your right. Defeat the Skaafin and the Factotums that get in your way. Soon enough, you'll find Gascone, who summons an exceptionally powerful Skaafin to assist him. 

:Moraz Goldtongue: "You summon me again? I grow tired of this, mortal!"
:Chancellor Gascone Dusant: "Enough talk, you horn-capped buffoon! Just help me!"

Defeat Moraz Goldtongue and confront Gascone, who surrenders, outside the Terminus. He tells you all about his deal with Clavicus Vile and the mess with the artifact, and that he was doing it because he thinks Sotha Sil is a shoddy leader.

:''"Yes, my methods were… unconventional. I admit it. But you have to understand—I didn't do this for me! I did it for the City.
:''Look around! Blood-thirsty fabricants, barren wastes, crumbling towers …. This is all Sotha Sil's fault!"
:How is it Sotha Sil's fault?
:"He abandoned us! While he tinkers away in the Centralis, we scrape by, eating nutriment paste and hiding from killer machines. Is that fair? Should we thank him for that?
:My eyes are open. The people of Clockwork City deserve better."

You have the chance to either kill him or spare him. Make your decision and head on over back to the Brass Fortress to inform Varuni of what's transpired and receive your reward for this quest.
  

Quest Stages