Travel to Chillwind Camp in the Western Plaguelands and meet up with your contact, Flint Shadowmore.
The only information we have thus far, then, is that Nathanos Marris may have been slain by this Blightcaller. We assume the Blightcaller is the same fiend that disposed of my agents.
Flint Shadowmore, another SI:7 operative, is stationed at the Alliance encampment of Chillwind Point in the Western Plaguelands. Seek him out; he will debrief you on the current situation in the Plagues and give you an assignment.
Good luck, [player].