Killing the Messenger

I make it my business to know what is going on within my district. Traditionally we use stone fiends to relay messages, but my informants have alerted me to some suspicious communications going on within the Old Gate. A venthyr has been hired to run missives between two undisclosed parties. When someone puts that much effort into concealing their identity, it can never be good. Find this courier and recover whatever missives they might be carrying.