Online:Blood of the Past

Quick Walkthrough
#Reach the gates of Castle Thorn and kill the guard dog.
#Explore Castle Thorn and destroy the Blood Twilight.
#Hunt for Lady Thorn and defeat Vaduroth and the traitor.
#Reach the Grand Cathedral of the castle and confront Lady Thorn.
#Talk to Gwendis.

Detailed Walkthrough
 
Picking Up the Quest
After entering Castle Thorn, head up the path and you will see two vampires, Gwendis and Talfyg. Gwendis will have her weapons drawn and Talfyg will be standing with his hands clasped together in front of him. As you approach, they will begin to speak.
:Gwendis: ''"Seems fairly quiet here so far, Talfyg. You're not misleading me, are you?"
:Talfyg: "I swear, what I told you is true. I see no need for this distrust between us."
:Gwendis: "Showing me a spooky castle proves nothing, Talfyg. Get us inside without drawing attention, then I'll decide how to feel about you."
:Talfyg: "Then maybe we could move faster, hmm? I'd like to get in before the fiends see us."''

This will mark the end of their conversation. A quest marker will appear over Gwendis's head. Speak to her. You will have the following conversation.
:''"What excellent luck. Never thought I'd see your face ever again. But here you stand, just when I need you. If you can believe it. I'm trying to stop another vampiric threat endangering all of Tamriel. Don't pretend to act surprised."
:What vampire threat? Why are you two here?
:"I could ask the same of you. But I don't really care. The ruler of this castle, one Lady Thorn, apparently decided to start amassing her own vampiric army. Bad move on her part. I want to know what she's planning, and then stop it."
:And what about your companion?
:"This worm of a fellow found me in Solitude. Insists he just escaped this place and needs to show me what the Lady's up to. The problem is I can't sneak in my usual way with him in tow. Hey, since you're here, feel like helping me storm a castle?"
:I'll help you get inside the castle and uncover Lady Thorn's plan.
:"Talfyg claims there's a secret door that he and I can use to slip in. But Lady Thorn's creatures heavily patrol the area around it. If you fight your way past the front gate, the racket should draw them away. This is going to be fun."''
Before you leave, you can ask Gwendis more questions about why she is here, about Lady Thorn, and about Lady Thorn's intentions, but they are not necessary for quest progression.

 
Distracting Lady Thorn's Creatures
Continue up the twisting path. As you approach the first group of enemies, Gwendis will address Talfyg behind you.
:Gwendis: "All right, that should draw the patrols. Now show me this secret door.
:Talfyg: "Yes, this way. And step quietly. The stones have ears."
Take down the first group and continue up the path. As you round the corner, there will be another group of enemies. Dispatch them, and proceed to the front gate. One more group of enemies will be waiting there for you, consisting of a Thorn Legion Senche-raht and two Bloodfiends. After you kill them, head through the gate and into the Castle Courtyard.

Standing in the center of the courtyard is the first boss, a very bad dog named Dread Tindulra. Its three main attacks are a cone of fire that it breathes from its mouth, an upward volley of fireballs that, after landing on the ground, will become small, burning AOE rings, and a roar that can summon multiple Death Hound Broodlings. Once the boss is dead, head through the door on the other side of the courtyard.

 
Uninvited Guests
You will enter into a hallway that opens into a large, great-hall-like room. Long ponds full of purple flowers border the room on either side, and another group of enemies waits for you in the center. As you enter the larger room, an unfamiliar voice will speak to you.
:Lady Thorn: "Uninvited guests! In my home! Please forgive my hospitality. I have not entertained in centuries."
Kill the group of enemies and proceed to the other side of the room. At the top of the stairs, another Senche-raht will be waiting. Kill it as well, then continue on through the door it had been blocking. Follow the hallway left around the corner, dispatch the next group of enemies, and head up the stairs. At the top, go right, head to the end, and turn left up the set of stairs. Head through the door on the right. It will take you into the Garden Conservatory.

You will enter into a large, square room with a smaller square pit in the middle that has stairs leading down into it in ever corner. Gwendis and Talfyg will enter with you, Gwendis with her daggers drawn and Talfyg with his arms crossed, and the following conversation will take place around you.
:Lady Thorn: "Well done, Talfyg. You brought me a daughter of Verandis, as requested. She will complement our lord's army well."
:Gwendis: "What is this? Damn it, Talfyg, what have you done?"
:Talfyg: "Your blood flows strong, Gwendis! My lady has need of you. But she has no use for the others."
While they speak, the second boss, the Blood Twilight, will appear in the middle of the square pit, and Talfyg will escape in a cloud of smoke.
:Gwendis: "No! You won't get away so easily!"
:Gwendis: "You can handle this. I refuse to let him win!"
She will turn into smoke as well, and you and your party will be left to fight the Blood Twilight.

The Blood Twilight can summon several Blood Channelers, which will tether to it with a red beam. It can go invulnerable, fly up above the pit, and fill the pit with a storm of blood that will quickly kill you if you stand in it for too long. Keep to the upper floor during this phase, avoiding the ghostly versions of the boss that will send a wave towards the center, which will push you back into the pit. Reanimated Vampires will spawn on the upper floor with you, and they have a heavy attack that must be dodged. Do so if necessary. Avoid the blood bubbles as well, which will occasionally be thrown onto the ground and explode after some time. After this phase, the Blood Twilight will become vulnerable again and return to the ground inside the pit.

Once the boss is dead, Gwendis will appear again in front of the door on the north side of the room, opposite to the one you came through.
:Gwendis: "Talfyg … got away."
:Gwendis: "He moved so fast …. Just caught me by surprise."''
You may speak to her here if you wish to learn more about what happened and where to go from there, but it is not necessary for quest progression.
When you are done, proceed through the door behind her into the Southern Training Yard.

 
Clearing the Way
The Southern Training Yard is the largest area in the dungeon so far. Groups of enemies are sprinkled around, and a number of Vaduroth's Sickles, purple, glowing scythes that are lodged in the ground, are nearby. The are useful for a mechanic on the upcoming boss, but they are not necessary here. Proceed down the path and to the left, killing enemies as needed, until you reach another door on the northern end of the training yard that leads to the Northern Training Yard. More enemies and sickles await you here. Proceed to the right, passed the fountain. After you have defeated the group of enemies near the fountain, you may hear Lady Thorn speaking to you again.
:Lady Thorn: "Such power! Perhaps I should not let my pets tear you limb from limb. Vaduroth can take your soul, instead."
Beyond the fountain is another door that leads to the Sanctuary of Lament. Enter through it.

At the bottom of the steps is another large square room, this one with the bodies of various creatures and people hanging from the ceiling on large hooks. There is a table in each of the four corners with a dormant Reanimated Vampire lying atop it. Vaduroth, the third boss, is near the door on the other side of the room. He will occasionally throw a sickle, which will draw all party members towards it and charge them with an AOE that will explode after a few seconds. The effects of this will stack, so try to avoid standing next to your party members. After this, one of you can stand in the circle under the sickle and use it on one of the corpses on the ceiling. It will spawn two Virulent Viscera, which will rush in and assist you. 

Vaduroth has the ability to summon his own Virulent Viscera. When he does so, he till teleport high above the ground and drop a large one under him. Over the course of the fight, the Reanimated Vampires will awaken too. Be mindful of them and their unblockable heavy attack as you take down the boss.

Once you defeat him, Gwendis will join you, appearing near the door Vaduroth had been blocking.
:Gwendis: "Gods above... what vile evil is this?"
:Gwendis: "I think I know where to find Lady Thorn. Push on to the cathedral while I search for clues here."
You have another opportunity to speak to Gwendis, this time to ask about why Lady Thorn would reanimate dead vampires and what Gwendis herself is looking for, but it is again not necessary to the progression of the quest.

When you are ready to move on, head through the door behind her, which will take you into the Castle Keep.

 
Storming the Keep
Proceed down the hall and into yet another large room, this one with an iron-wrought fence surrounding a pool in the center. You will encounter another group of enemies down the stairs on your side, and then up the stairs and to the left on the other side. Continue through this area and turn right, heading up the stairs. Another group of enemies awaits you that includes a Seething Gargoyle. These will appear in the fourth boss fight, and they also have an unblockable heavy attack that you need to dodge.

Once the gargoyle and its friends are dead, go down the hallway it was blocking, and follow it to the right. At the end, turn left, climb the stairs, and turn right. There will be a door at the top of a smaller set of stairs that leads to the Castle Exterior. Pass through it.

Follow the road. There will be three more groups of enemies to deal with on the way, the last one containing two more of these Seething Gargoyles. Once you defeat them, pass through the door into the Statuary Garden.

You will enter upon a round courtyard with Gwendis, and Talfyg will be waiting for you in the middle. As you approach, he will speak to you, his voice distorted.
:Talfyg: ''"How dare you reject Lady Thron's offer? Look! Tremble before the power you might have wielded!"
He will then transform into a monstrous Bloodknight.
:Gwendis: "Well this explains some things. What have you become Talfyg?"
:Gwendis: "There's no running away this time, monster!"''
You are now ready to fight the fourth boss: Talfyg.

Talfyg has the ability to summon Volatile Hounds, which spring from the ground, as well as Seething Gargoyles, which have been encountered before, and a new type of Gargoyle, the Frozen Gargoyle. These will slowly walk towards Talfyg, with an AOE of swirling ice under them. Another mechanic to watch out for is Talfyg's Annihilate attack. He will lift an arm into the sky and beams of bright red will shoot from his hand, creating a small blood AOE underneath every member of your party. Keep moving during this phase and try not to overlap with your party members. He will also occasionally slam the ground, creating a bloody AOE underneath himself that will persist on the stage for some time.

Once he is dead, Gwendis will appear on the other side of the arena.
:Gwendis: "Glad to be rid of that worm. He deserved worse."
:Gwendis: ''"The cathedral isn't too far ahead. Lady Thorn should be inside."

Once again, you have the option of asking Gwendis a few questions, this time about Talfyg, but this is not necessary for quest progression.

Proceed through the open gates beside her and up through the next door, leading to the Battlements.

 
The Home Stretch
Head along the "C" shaped Battlements, defeating more groups of enemies on your way to the cathedral. There are four groups blocking you path, the first on the first raised platform, the second on the bridge to the second raised platform, the third on the second raised platform itself, and the fourth in front of the door leading into the cathedral. Defeat them all, then head through the door and into the Cathedral Narthex.

Head through the open doorframe and into the next large room, and kill the group of Bloodfiends feasting on the corpses there. Once you kill them, Gwendis will join you.

:Gwendis: "You found what remains of the prisoners. Such brutality."
:Gwendis: "Wait … look at all these documents."
She will run over to a desk and nearby dresser, both covered in papers and alchemical equipment.
:Gwendis: "There's information here about Lady Thorn... and the Gray Host. I need to study this."

She will bend over and start looking at them, and you may speak to her if you like, but it is not necessary. Proceed through the doorway on the west side of the room when you are ready, then turn left and climb the stairs. At the top, turn right, and pass through the door to the Grand Cathedral.

 
Lady Thorn
As you pass through the door, you will come upon the final boss, Lady Thorn herself. She stands, in Vampire Lord form, in the middle of another large, square room. She will take flight once she is engaged. She can summon motes of blood from the ground with a large AOE circle under them that will either explode or move away from her, summon a storm and a protective AOE you must stay inside. The AOE can move around the arena, and, during this phase, Lady Thorn will periodically perform a Blood Dive, diving towards you from a different corner of the room and swiping her claws. Blood Scavengers will spawn along the outsides of the arena, and, when killed, will drop a mote of Blood Corruption that can be synergized with. Throw these motes at her, and, after a few, she will return to the ground.

She has another attack called Scatter, where she will dive into the ground, creating a AOE, and send numerous black storm AOEs spiraling out from where she disappeared. She can keep spawning the exploding motes during this phase. When the phase ends, it will be telegraphed by the appearance of another large AOE that, upon exploding, she will reappear from.

Once she is dead, Gwendis will join you, appearing by the door you entered through.
:Gwendis: "It's over. The ancient clan of Lady Thorn is no more. Good riddance."
:Gwendis: "I need to speak with you about what I found in those documents."

Go speak to her. You will have the following conversation.
:"An undead army shattered, an evil Vampire Lord destroyed, and a monstrous I-don't-know-what banished back to Oblivion. You do incredible work. Seriously, I don't know what might have happened if you weren't here. Thanks."
:What's next for you?
:"My next step is contacting House Ravenwatch to tell them what we found. Lady Thorn's connection to the Gray Host needs deeper investigation. Before I go, I'd like you to take this. Without you, I might be up on one of those hooks. Thanks."''
With these words, you can then complete the quest and receive your rewards. You may continue speaking with her, and ask her about Lady Thorn's plan to build the army or what she thinks House Ravenwatch will do with the information if you so desire.
 
 

Quest Stages