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Two days after Kerrigan defeated her former allies on Korhal, a huge wave of UED-controlled zerg appeared in orbit over Tarsonis; hundreds of them landed on the planet and began to attack Kerrigan's outposts. Infested Duran offered to rally the troops. Kerrigan gave him her approval, stating that after they secured the perimeter, they would take the fight to the renegades' hive clusters.
Initially the battle went badly for Kerrigan's forces. Kerrigan lost four of her five primary hive clusters - only the center one survived, and it was nearly surrounded by the UED Slave Broods. As Kerrigan slowly fought back, Duran noticed a UED Science Corps outpost at the rear of the landing zone. There were a number of scientists and genetic engineers present, protected by security guards and pyrotechnic engineers, along with a number of zerg locked up in pens. Kerrigan commented that the UED's control of the Second Overmind was tenuous and it could not directly control the zerg on Tarsonis. These "scientists" were needed to coordinate the attack.
Duran ordered the Cerebrate to attack the scientists instead of wiping out the attacking zerg. Kerrigan's Swarm slowly fought its way past the UED's zerg, breached the UED compound's defenses, and killed all 30 scientists. The imprisoned zerg were then freed from their pens. The Slave Broods brought to Tarsonis also turned against their former masters, forcing the UED to flee.
Tarsonis remained under Kerrigan's control. Any leftover renegade zerg on the planet were either destroyed or captured.