Death Incarnate

Walkthrough
The quest begins automatically when the Dragonborn returns to the Dark Brotherhood Sanctuary after poisoning the Emperor's decoy in To Kill an Empire.

Enter the Sanctuary
Returning to the Sanctuary, it quickly becomes clear that not all is well. The rising smoke, the many barrels of burnable liquid and the crucified body of Festus Krex make this immediately clear.

Apparently the Emperor's elite guard, the Penitus Oculatus, was able to track down the location of the Dark Brotherhood Sanctuary and are going about systematically wiping out the Dark Brotherhood members and the Sanctuary.

Search for survivors
Inside there are more of these agents, and the heavy smoke makes it very difficult to see and orientate. The dead bodies of Arnbjorn and Gabriella, along with the dead tame spider Lis show that the Penitus Oculatus really must have surprised their victims.

Kill the Legion soldiers inside the Sanctuary
Even though the Sanctuary is becoming more and more hazardous, there are still quite a few agents about that needs to be wiped out, for there to be hope of saving any of the Dark Brotherhood members.

Kill Nazir's attacker!
Further into the Sanctuary, in the dining room, a soldier is attacking Nazir, help him out.

Speak with Nazir
Nazir explains the sudden attack, and that almost no one survived.

Escape the Sanctuary
Trying to escape, the Dragonborn is trapped in the room with the Night Mother's sarcophagus.

Embrace the Night Mother
Embracing the Night Mother, her sarcophagus shuts, protecting the Dragonborn, as it falls through the large window into the water pool in the main cave. Thus saving the Dragonborn from burning to death.

Luckily Nazir and as it turns out Babette pull the sarcophagus onto the shore, and save the Dragonborn.

Talk to Astrid
Only to drop the bomb shell, it was actually Astrid who betrayed the Dark Brotherhood to the Penitus Oculatus, jealous of the Dragonborn's status with the Night Mother. Astrid admits to her betrayal, and deeply regrets her transgression.

Kill Astrid
The massively burned and dying Astrid asks the Dragonborn to kill her.

(Optional) Retrieve the Blade of Woe
The Blade of Woe lying next to her may be used to put her out of her misery.

Return to the Night Mother
Return to the Night Mother, and she will inform the Dragonborn that the assassination of the Emperor is still on, and that the next step is to talk to Amaund Motierre in Whiterun again, and to find out where the real Emperor can be found. Thus begins Hail Sithis!. Wettlauf mit dem Tod