In the distant Koprulu Sector of the galaxy, human colonists known as the Terrans have established competing governments far from Earth after their colony ships went off course centuries earlier. Two alien species also inhabit the sector: the Zerg, a ravenous insectoid swarm driven to assimilate other organisms for genetic perfection, and the Protoss, an ancient and powerful race that has secretly observed the Terrans for years.

When the Zerg begin targeting Terran worlds to absorb their psionic potential, the Protoss respond by destroying infested colonies to prevent the swarm's spread, plunging all three factions into open conflict. As the Terran Confederacy crumbles under attacks from rebels, Zerg, and Protoss alike, a new authoritarian government rises from the chaos while the Zerg Overmind sets its sights on the Protoss homeworld, seeking to assimilate the one species that could grant it genetic perfection.