Many months after the Battle of Mount Hyjal, The Lich King began losing his power. With it, he also lost control over much of the Scourge. Detheroc and his brothers, Varimathras and Balnazzar took control over these undead and usurped control of Lordaeron from King Arthas Menethil.
In addition to commanding undead, Detheroc used his telepathic powers to take command of the New Alliance, commanded by Grand Marshal Garithos. He established a well-fortified stronghold in the Western Plaguelands
Detheroc's stronghold was besieged by the Banshee Sylvanas Windrunner with the aid of Varimathras, who had sworn allegiance to Sylvanas in exchange for his life, much to Detheroc's anger. Sylvanas defeated Detheroc's forces and tore the Dreadlord to "bloody shreds". Garithos and his forces were then freed and allied with Sylvanas to strike against Balnazzar.