*a short, hastily written note is inside*

Servants of Kelemvor,

We need to speak. I would inform you now, but it is better to not write down. Seek me out about Sanctuary. Grigorii

Izarious reads over the letter and randomly has it returned to the Last Stand, hoping for the best.

No letter is returned. Anton has either fled to the surface, is taking his letters elsewhere, or is no longer alive.

Dredging the bottom of the Black Lake or searching the bowels of the Mausoleum wouldn't be bad ideas.