In the aftermath of the events of the Third War, Prince Arthas shattered the Frozen Throne and became one with the Lich King. Deep inside the fortress of Icecrown, he then sat on his throne in quiet meditation and the people slowly began to forget the threat that was waiting on the third continent of Azeroth called Northend. But the quiet times are over as the Lich King is now awake again and sends his Scourge armies out to every corner of Azeroth. At the same time the blue Dragon Aspect called Malygos also emerged from his long seclusion and launches a merciless war against mortal practitioners of arcane magic. Now both the Horde and the Alliance amass their armies and make their move into Northend in the hopes of keeping the threat in check and perhaps even finally destroy it.
Besides the whole new continent of Northrend with new zones, enemies, factions, instances and hundreds of quests, the second add-on to World of Warcraft also adds the first hero class to the game: the Death Knight. A Death Knight can be created on every server the player already has a level 55+ character on, can be of any race and is very powerful because he can do almost everything except for carrying shields or using ranged weapons. Once the player has created a Death Knight, he begins his life at level 55 in an instanced area on a necrophyle under the watchful eye of the Lich King himself. During the following quest line, the player will not only learn how to enchant his sword by using runecrafting, he will also slowly become disgusted with the ways of the Lich King and in the end desert him to enter the normal world of Azeroth and Outland and join up with the Alliance or Horde in the fight against the Lich King.
The expansion also expands the level cap to 80. In correspondence with that new talents are available for each class to invest the 10 additional points in and many trees were rebalanced to accompany the new talents. Another addition is the new profession called "Inscription". People of that profession can produce Glyphs that are not applied to an item but instead alter the effects and/or requirements of spells and abilities of their carrier. A druid can for example use a glyph to increase the duration of his "Thorns"-buff from 10 minutes to 60 minutes or decrease the amount of mana required to cast "Gift of the Wild".
Other new features are new pvp battlegrounds and arenas, the addition of Barbershops, which allow the players to change their appearance after character creation in exchange for gold, an Achievements-system and an in-game calendar.