Draenor, the homeworld of the orcs, is being torn apart by a mysterious force known as fel magic. Gul’dan, a powerful orc warlock, unites the orc clans and forms the Horde, and creates a portal to the world of Azeroth. The orcs begin to use fel magic to drain the life out of captive draenei in order to sustain the portal. Once it is operational, Gul’dan leads a small warband to capture prisoners on Azeroth and sacrifice them to bring the rest of the Horde through the portal. Durotan, the chieftain of the Frostwolf Clan, his pregnant mate Draka, and his friend Orgrim Doomhammer join this initial warband. While crossing through the portal, Draka goes into labor. When the orcs arrive on Azeroth, Gul’dan assists Draka with giving birth, but the baby is stillborn. Gul’dan then drains the life out of a nearby deer to revive and infuse fel magic into the baby, which Durotan later names Go’el.
The orcs raid several settlements throughout Azeroth. Anduin Lothar, the military commander of the human forces in the Stormwind Kingdom, looks over some of the men that were killed, and finds a trespassing mage named Khadgar, who explains that he was investigating the dead bodies because they contained traces of fel magic. Khadgar persuades Stormwind’s king, Llane Wrynn, to consult Medivh, the renowned Guardian of Tirisfal, and Llane sends Anduin and Khadgar to Medivh’s stronghold, Karazhan, to inform him of the fel magic’s presence on Azeroth. In the Karazhan library, a ghostly shadow leads Khadgar to a mysterious book, which he takes.
Anduin, Khadgar, and Medivh join a scouting team following traces of fel magic, but are ambushed by orcs. Medivh uses a spell to kill the fel-corrupted orcs, leaving the Horde’s warchief, Blackhand, to flee along with Durotan and Orgrim. Khadgar restrains a half-orc slave, Garona, and the soldiers take her prisoner. King Llane frees Garona in exchange for loyalty to Stormwind, and she leads the humans to spy on the orc camp, where they learn of Gul’dan’s plan to bring the Horde to Azeroth. Meanwhile, Durotan realizes that the fel magic is responsible for the destruction of Draenor, and if Gul’dan is not thwarted, Azeroth will suffer the same fate. Despite Orgrim’s objections, Durotan invites Llane to a secret meeting so that the Frostwolf Clan and the humans can unite to defeat Gul’dan. While studying the book he took from Karazhan, Khadgar learns that Gul’dan could not have opened the portal on his own; he had help from someone on Azeroth. He is confronted by Medivh, who burns Khadgar’s research when Khadgar offers to help him with his work.