In the House of Ashes #4 | Chapter 8 Dark Messiah Guide

Come back to the laboratory. On the corner is hatch to the underground. Go there. One of the corridors is locked by the bar. Use Laboratory Trap Door Key to open it. Behind the bar you will find magical Frozen Daggers. Take them and climb up the ladder. Go upstairs. There are Necromancers - kill them.

Hatch to the underground	Use the Laboratory Trap Door Key to open the bar.
Souldrinker Daggers	Climb up the ladder.
Go upstairs.	Don't give up!

Go on and kill all enemies. Go upstairs. You will hear a voice - that's Leanna! One of the Black Guard's is precipitating her into the gap. Go to the gallery, and run down through the first stairs on the left. Kill two Necromancers, take items from wooden box and come back to the gallery. Turn left and go upstairs.

The signs of blood...	Kill all enemies!
You'll hear voice...	Leanna!
There are many of Necromancers and Acolytes...	Wooden box
Turn left.	The enemies are still appearing...

You'll come to the huge chamber. Set up Fire Traps and go further. Kill all enemies and go inside. You will see the execute stage... Full of blood...

Black Guard. He is one of the most important of them.	Necromancer
It's really a huge building.	You will see the light from far... that means only one: troubles!
There are many of enemies...	Turn left.
The execute stage!	Wooden box