Lab Rat

Lab Rat is the first mission in StarCraft II: Heart of the Swarm.

Background
Having been abandoned to the zerg at New Gettysburg by her superior, Sarah Kerrigan was captured and infested by the Overmind as part of the creature's scheme to undermine his creator's malevolent plans. While in the service of the Overmind, Kerrigan found the means to undo her ghost conditioning.

With the possibility that the xel'naga device, meanwhile assembled, could revert zerg infestation and warned by Zeratul of the catastrophic outcome inevitably tied to Kerrigan's death, Jim Raynor traveled to the zerg homeworld of Char and used the device to de-infest the self-titled Queen of Blades. However, most of her psionic ablities remained intact.

The Mission
Sarah Kerrigan was taken to a research station under the Umojan Protectorate. Despite claiming to have little or no memories of her deeds as the Queen of Blades, Valerian Mengsk wished to test her abilities to control the zerg. He gave her a drone and had her create a small hive cluster, taking the test a little further than planned. Kerrigan then began disobeying his instructions, creating numerous zerglings. After using the beasts to destroy a portion of the complex, her point, though it angered and annoyed him, was thoroughly grasped by Valerian.

Aftermath
"Luck had nothing to do with it. And maybe now you understand how dangerous the zerg are. I'll send them back to their pens. I appreciate that, I'm opening your cell right now, if you'd like to join me. And perhaps next time you can make your point without destroying half the facility?"

- Sarah Kerrigan and Valerian Mengsk on the aftermath of the "experiment".