After his arrival at Daggercap Bay, Arthas led his troops through the hills of Northrend in search of a place where they could set up a base camp. Despite the local tribe of ice trolls' opposition, Arthas made his way further into the mainland, and spotted a gold mine. He was ambushed by Muradin Bronzebeard and his band of Dwarven riflemen. Muradin recognized his old friend and student Arthas, and ceased fire, thinking that he had come to rescue him from the attacking undead. Arthas told him that he was hunting Mal'Ganis and didn't know that Muradin was in Northrend too, so they decided to join forces.
Muradin told Arthas that his main base camp was North, surrounded by the undead and withstanding a heavy siege. Arthas rallied his troops and fought his way to the Dwarven town.
At this time the scouts reported a massive undead bastion to the West, where possibly Mal'Ganis was hiding. Arthas led a decisive assault and, with the help of Muradin's dwarves, the undead base was destroyed.
However, Mal'Ganis had yet to be accounted for.