Even though Raynor’s Raiders and prince Valerian’s forces were able to neutralize the Queen of Blades and cripple the Swarm, a vast number of zerg hives still remain on Char. Without the Queen of Blades' unifying presence, some zerg queens have begun to take control of individual zerg broods.
Kerrigan returns to Char determined to reunite the Swarm under her control. Before her defeat, the Queen of Blades hid caches of eggs on the planet; gathering these eggs and returning them to the spawning pools to hatch will allow Kerrigan to quickly grow her numbers. There is, of course, a catch: one of the rogue queens is collecting Kerrigan’s unhatched eggs as well and spawning them as her own. The only way to ensure Kerrigan’s victory is to hatch as many eggs as possible and to use superior numbers to subdue the rogue queen.
The zerg are able to infest almost any world they encounter, a testament to their amazing ability to adapt to the universe's most extreme environments. The planet Kaldir is one such environment. Its extreme cold and frequent flash freezes make this one of the most inhospitable worlds in the Koprulu sector... which is exactly what sparked the Queen of Blades’ interest in Kaldir. Hoping to make the Swarm stronger by evolving a way to deal with extreme cold, she sent a brood to infest Kaldir. However, the brood never reunited with the Swarm.
On Kaldir, Kerrigan’s objective is twofold: learn to adapt to the withering cold, and discover what happened to the lost brood. Before long, you will learn the brood's fate... and when you do, the cold of Kaldir will be the least of your worries.