Note from Carnius is a missive addressed to the Nerevarine instructing the betrayal of a collaborator.
At the request of Carnius Magius the Nerevarine teams with Hroldar the Strange to murder Tirvel Balen, a messenger sent to deliver a status report on activities at the Raven Rock ebony mine. Following Tirvel's death the Nerevarine receives this note from Hroldar.
Reading this, you've successfully completed my little task for you. Before you return, however, I have one last deed for you. Hroldar should've given you a few scrolls along with this note; since he can't read, he won't realize that I intend for you to kill him.
The scrolls should grant you control over his wolves long enough to put an end to him. You don't need to know the details; only that I can no longer trust him and that his usefulness to me is at an end. I'd do the job myself, but then... that's what I have you for. Why take risks, when someone else can take them for me?
I expect you to return shortly. Do not keep me waiting.