Draenor, the home-world of the orcs, is being torn apart by a mysterious force known as Fel magic. Gul'Dan (Daniel Wu), 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 war-band to capture prisoners on Azeroth and sacrifice them to bring the rest of the Horde through the portal. Despite their doubts, Durotan (Toby Kebbell), the chieftain of the Frostwolf Clan, his pregnant mate Draka (Anna Galvin), and his friend Orgrim Doomhammer (Robert Kazinsky) join this initial war-band. 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 (Travis Fimmel), 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 (Ben Schnetzer), who explains that he was investigating the dead bodies because they contained traces of Fel magic. Khadgar persuades Stormwind's king, Llane Wrynn (Dominic Cooper), to consult Medivh (Ben Foster), 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 war-chief, Blackhand (Clancy Brown) to flee along with Durotan and Orgrim. Khadgar restrains a half-orc slave, Garona (Paula Patton), and the soldiers take her prisoner. Garona tells Meedivh that a dark daemon showed Gul'Dan the path to Azeroth.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. Both Anduin & Khadgar suspect that Medivh was the one who opened the portal gates for Orcs on the Azeroth side.The Frostwolf Clan meets with the humans to negotiate an alliance, but the group is ambushed by Blackhand. As the humans retreat, Medivh forms a magical barrier to protect them, but Lothar's son Callan (Burkely Duffield) is separated from the rest of the group and killed by Blackhand. Medivh is severely weakened, and Garona and Khadgar take him back to Karazhan to recover. After noticing Medivh's eyes shine green, showing that he is infected by Fel magic, Khadgar returns to his former home, Dalaran, to seek help from the Kirin Tor, the authority of human and high Elven Mages.The Kirin Tor facilitate a meeting with Alodi, revealed to be the shadow who led Khadgar to the book; she confirms that Medivh has indeed been corrupted by Fel magic and possessed by an unknown demon. At the orc camp, Blackhand purges the Frostwolf Clan. Orgrim helps Draka to escape, and she sends Go'El down a river in a basket, but is then found and killed by another orc.Durotan challenges Gul'Dan to Mak'Gora, a traditional Orcish duel to the death for leadership of a clan - in this case, all of the orcs. During the fight, Gul'Dan violates the honorable combat rules by draining the life out of Durotan with his magic, killing him and earning the disapproval of the orcs watching, and he empowers Blackhand with the same magic. Medivh, now in a half-demonic state, starts to open the portal to Draenor, and Gul'Dan sacrifices the captured human villagers to allow the rest of the Horde to enter Azeroth.Llane leads the human army in an assault on the orc camp, while Anduin and Khadgar fight Medivh and destroy the demon that had begun to manifest on the outside. Medivh is left mortally wounded, and uses the last of his strength to close the portal to Draenor and instead open a portal to Stormwind, allowing Llane to evacuate most of the freed prisoners. When Medivh eventually dies, the portal closes, leaving Llane, Garona and a small number of human soldiers to fight the orcs. Llane secretly orders Garona to kill him, bringing her honor among the orcs and putting her in a position of power to bring peace between the two races.Garona reluctantly does so, and is welcomed into the Horde by Gul'Dan. As the orcs celebrate, Anduin arrives to retrieve King Llane's body and discovers Garona's knife in the body, realizing that it was she who had killed their king. Blackhand challenges Anduin to Mak'Gora, and Anduin quickly disposes of him. Against Gul'Dan's demands, the orcs, bound by tradition, allow Anduin to depart with Llane's body. At Llane's funeral in Stormwind, the leaders of the other human nations, along with the high Elves and Dwarves, proclaim an alliance against the orcs and rally behind Anduin as the leader of the Alliance forces. Elsewhere, Orgrim takes one of Durotan's tusks to one day give to Go'El, and the basket containing Go'El is found by a human.