Online:A Keep's Ransom

Quick Walkthrough
 
#Speak to Commander Axius outside Borderwatch.
#Enter the sewer beneath Borderwatch.
#Find and talk to one of the infiltrators.
#Locate Seeks-the-Dark and talk to him.
#Rescue the hostages from the southwest guard tower and talk to Calixto Tunifus.
#Rescue the hostages at the smithy and talk to Shanil-Tee.
#Rescue the hostages in the stable and talk to Otten.
#Escort the hostages to the sewer entrance.
#Rescue the Ayleid Scholar from the keep.
#Find the crypt key within the keep
#Enter the crypt with Seeks-the-Dark.
#Find and enter the Ayleid ruin.
#Stop the Painted Eye ritual.
#Confront the Painted Eye leader.
#Escape the Ayleid ruin.
#Speak to Seeks-the-Dark and Erilthel.
#Speak to Commander Axius.

Detailed Walkthrough
You can start the quest by either talking with Brigadine Scout Iscaria or talking with Commander Axius. If the former, she will direct you to her commander to expain the situation.

It seems that Borderwatch was overtaken by a mysterious faction called the Painted Eye, who have taken several hostages and will kill them if any of their demands are not met. As seen in the nearby Demands of the Painted Eye, these demands are near impossible for Commander Axius to meet. He suggests that you can infiltrate the keep by entering through the sewer, but warns that the two infiltrators who went in prior to you have not been heard from since.

Once you've found the entrance to the sewer in the wilderness surrounding Borderwatch, you'll have to search the sewers. To do so, you may have to kill the Painted Eye agents. Suddenly, you hear a voice cry out in the sewers, which could be one of the hostages. Following the voice to a nearby side room you will find a Bosmer woman stamping on some dead skeever. This is Erilthel, one of the infiltrators who entered the keep before you. Speaking with her, she will explain how they got involved with hostage situation and how her companion Seeks-the-Dark lured the Painted Eye away when they were about to find her.

She will ask for your help to rescue him, Erilthel will then join you to search the sewers. Fighting the animals and patrolling Painted Eyes, you will have to go eastward through the sewer until you reach the door to the Borderwatch Cellars. Erilthel will mention that she hasn't been here before and it would be a good place to check. Inside the room, you will find an Argonian locked in a cage. This is Seeks-the-Dark and he is annoyed to see Erilthel came back:
:Erilthel: ''"Seeks! Hold on, I'll get the lock!"
: 
:Seeks-the-Dark: "Erilthel! I told you to run!"
:Erilthel: "I did, but then I ran into our friend here and-hey, did you let yourself get caught so I could get away?"
:Seeks-the-Dark: "Pfft, unlike you I know when to make an escape. You. Come here. We need to talk."''

While Erilthel works on the lock, you can talk to Seeks-the-Dark who has a plan to free the hostages. He will ask you to find and free the hostages, while Erilthel leads them out and he acts as a distraction once more. He will suggest that you check the southwest tower first once you go top ground. 

Going through the door to the east, will bring you to the large courtyard for Borderwatch, various Painted Eye forces will be roaming the area. Despite Seeks-the-Dark saying to search for hostages southwest of the keep, on the map you will need to go East-Southeast from your location to reach the tower where three hostages are tied up. Calixto Tunifus, one of the hostages will have some information for you, firstly that the Painted Eye's demands are a ruse and that another group of hostages are being held at the smithy. You can then tell him, to head to the cellar entrance so Erilthel can lead them out.

To get to the smithy,  . Again, you'll be approached by an hostage, Shanil-Tee, to learn about the next location where fellows are being held. She indicates the stables.

To find the stables,  . Otten is too terrified to escape on his own and asks you to escort him to safety. He doesn't seem to know of other groups of hostages. Lead the last group to the sewer, then talk to Seeks-the-Dark who'll be waiting for you. To do so,  .

The Argonian is in fact a thief from the Guild sent to "retrieve" an Ayleid relic. He suspects that the Painted Eye might seek just the same. There's a scholar held captive in Borderwatch and Seeks wants you to free him, in order to better understand what the relic is. Teldundindo tells you that it's hidden beneath the chapel, but you'll need a key to unlock the area. The key  is in the commander's quarter. To reach the key, you'll need to  .

With the key in your hands (or backpack to be exact), you can head to the chapel and search for an entrance to the Ayleid ruins where the relic is hidden. Teldundindo talks to you about the chapel's tombs being the possible entry point of the ruins running underneath the complex. Enter the crypts by going to the northernmost building on the map. The area is recognisable by the tombs outside. Seeks-the-Dark will be waiting for you at the door, noting that Painted Eye agents are already turning the whole place upside down. Make your way through the dungeon. At the very end, there is a metal gate through which you can access the Ayleid ruin. 

You finally arrive at the ritual site. Three Attunement Crystals are maintaining it, and need to be destroyed. They are protected by Sister Ignatia and Brother gro-Mora. After defeating them and destroying the crystals, you can continue into the next room. Here, you will find the leader, still conducting the ritual. Erilthel causes a cave-in, crashing on top of the relic and effectively ending the ritual. However, you need to make your way out of the ruin before meeting an untimely death.

But you wouldn't be the hero everyone sees in you if a simple cave-in could mean the end of the journey. Once you have escaped, you can listen to Seeks and Erilthel's conversation:
:Seeks-the-Dark: "Erilthel."
:Erilthel: ''"I know. I said I wouldn't come back, but I heard yelling echoing up from a grate—and I was worried—so I followed—and it was slippery and—"
:Seeks-the-Dark: "Thank you. If it weren't for you, we couldn't have stopped the Painted Eye."
:Erilthel: "You mean it? It was a pretty dramatic entrance wasn't it? Maybe I should practice—"
:Seeks-the-Dark: "Don't push it."''

You can then speak with both of them, Seeks will announce the job as "a wash" with the failure of collecting the artifact. Despite having helped save the hostages, he won't go and collect a reward from Commander Axius as there will be too many inconvient questions. He instead asks that you tell the commander that the "infiltrators" died before you got there. When you speak to Erilthel, she will still be excited and enthusiastically tells you how she ended up falling through the ceiling. Once you have spoken with both of them, Erilthel will reveal that their original job wasn't such a wash after all:
:Seeks-the-Dark: ''"Now, I need to figure out how to tell the Guild that we didn't get the relic. They won't be happy."
:Erilthel: "What do you mean? I have the relic right here. Oh! Careful, still got bits of Painted Eye lady on it."
:Seeks-the-Dark: "What? When did you—"
:Erilthel: "When you were all: oh, look at the ceiling, it's coming down around us. This is why I should take the lead next time!"
:Seeks-the-Dark: "Absolutely not."

You can then go to Commander Axius tell him the situation has been dealt with. He will be standing outside the main gates of the fort:
:"I've got a camp full of liberated hostages, and my scouts tell me there's a significant drop in Painted Eye activity within the fortress. But I want to hear it from someone who's seen things firsthand. What's the situation in Borderwatch?"
:The Painted Eye's leader is dead and all the hostages are free.
:"Damn fine work. I'll get my troops together and we'll mop up the stragglers.  So much for those experts. You did the work of both of them. And most of us, for that matter! Borderwatch is in your debt. This is all the payment I could muster."''
Notes
Completing this quest will allow you to recruit some of Commander Axius' men to defend Fort Redmane during Pyre of Ambition.
 
Quest Stages