Blizzard has revealed the details of its first expansion pack for 2010’s top-rated strategy game, StarCraft IIHeart of the Swarm will continue the sci-fi story, introduce a new campaign and add bonus content to the multiplayer.

Heart of the Swarm will follow the story of “Queen of the Blades” Sarah Kerrigan, and put the focus on the Zerg — a race of insectoid aliens obsessed with assimilating other races to steal their genetic mutations. Finally, the trilogy will be completed when the Protoss-themed Legacy of the Void is released.

Swarm will introduce about 20 new single-player missions, with units and abilities that are only available in the campaign. Befitting of the Zerg’s genetic obsession, you’ll be able to evolve your swarms of insects to gain new abilities, subspecies, genetic mutations and evolutionary offshoots.

You’ll need Wings of Liberty to play Heart of the Swarm, but Blizzard says the price will reflect the game’s limited content and expansion pack branding. As for the game’s release date — Blizzard is using its tried-and-tested company line. “We will take as much time as is needed to ensure that Heart of the Swarmmeets the expectations of our players, as well as our own high standards.”