Vile, Lady Nightswood, and The Leaper would make excellent weapons in the fight against the Lich King if they can be broken from his will. That is what the Sovereign Rod is for.
You'll find them on the ledges to the east and west of the vault, as well as on the mid-tier of the vault above us. The rod is to be used upon the corpses of the three.
You have NOT turned them yet. Do not insult my intelligence, <class>!
Completion
We will put those three to good use once we finally take the vault.
Speaking of which....
Notes
Vile and Nightswood are stationary on their ledges (Vile to the right, Nightswood to the left), while the Leaper paths pretty much the entire middle level of the Vault.
Vile says: Vile free? Vile love <name>!
Lady Nightswood says: You dare? Where is Baron Sliver? I would have words with him!