Flint Shadowmore - (Step 3) Travel to Chillwind Camp in the Western Plaguelands and meet up with your contact, Flint Shadowmore.
Alliance & Horde
The Archivist - (Step 1) Travel to Stratholme and find Archivist Galford of the Scarlet Crusade. Destroy him and burn down the Scarlet Archive.
Stormwind City Alliance Quest
The Blightcaller Cometh - (Step 5) Return to Stormwind and inform Highlord Bolvar Fordragon of the fate of Nathanos Marris.
The Eastern Plagues - (Step 4) Scour the Eastern Plaguelands for clues as to the "Blightcaller" and the missing SI:7 agents. If you find any SI:7 Insignias, return them to Flint Shadowmore at Chillwind Camp.