Plaguelands: The Scarlet Enclave

Sometimes you just get the urge to kill someone, and sometimes, you have to kill someone in order to complete the quest Endless Hunger.

You've got some new snazzy weapons to stab people with, so now you'll need to forge some runes on them in Runeforging: Preparation for Battle.

You've made yourself a new Death Knight, but you kind of need a weapon to go with your looks, right? The Emblazoned Runeblade helps you with Runeforging.

In Service of the Lich King is a simplistic walk to another quest giver quest, but it also signifies the start to your Death Knight days.