StarCraft II: Heart of the Swarm is an expansion pack to science fiction real-time strategy game StarCraft II: Wings of Liberty and part two of the planned StarCraft II trilogy. Part three is titled Legacy of the Void. The expansion includes additional units and multiplayer changes from Wings of Liberty, as well as a continuing campaign focusing on the Zerg race. It spans 20 missions (plus several zerg unit evolution missions) and is priced as an expansion set.