Niadra was created by Sarah Kerrigan to slay the protoss on the Daelaam Ark as it tried to escape Kaldir in order to warn the protoss of Shakuras of Kerrigan's actions. During the battle, Niadra damaged the ship's propulsion systems and eliminated the protoss. Afterwards, Niadra lost contact with Kerrigan as the ship had gotten too far away, so Niadra settled her brood in the ruins of the ship, waiting for her return.
Niadra never heard Kerrigan's voice again, but her purpose remained, so she took her brood to the terran planet Adena in order to lay a trap for terrans so that she could grow the brood for a confrontation with the protoss. They were greeted by renegade Terran Dominion forces seeking to salvage a jorium mining base. Niadra infested the squad's commander with a larva just as Kerrigan did to create her for the Daelaam Ark, but this was destroyed by the Daelaam in orbit under Admiral Urun. Undeterred, Niadra turned her attention to a psionic among the terran's ranks named Elms, who she thought would help her brood grow.
The brood attacked Elms's marines, but Elm was able to psionically sense Niadra's orders and counter their movements. Admiral Urun arrived with a protoss force and pushed the brood backwards, but the zerg amassed for a counterattack.
They pushed through the protoss lines, with Niadra herself coming face to face with Urun, while Elms's forces encountered a group of their infestors in the caves.
While they were unable to implant a larva into Elms, one managed to slip into Gary. Meanwhile, Elms discovered that a large amount of zerg were in the cave, but the marines were able to escape when the caverns were collapsed.
Meanwhile, on the surface, Niadra's zerg tore into the protoss, who were being worn down. Several merged into archons to kill as many zerg as possible before falling, but in the end Niadra confronted Urun and impaled him on her talons. With the protoss defeated, Niadra turned her brood on her true prize: Elms and the escaping terrans.
However, Elms and her group escaped through the hanger bay, though the brood was able to kill Carter with an acidic burst. The brood sent infestors to impede their progress, but they were gunned down. As Elms and her squad made it to the dropship, Niadra attempted to psionically assault Elms, but she was knocked unconscious by Yong. As the terrans escaped her clutches, Niadra began to formulate a new plan to destroy the protoss.
The larva that made it into Gary would later bear fruit, as during a transaction in the Last Junction where Elms and her crew tried to sell the jorium, Gary fully mutated into an infested terran. Shouting his allegiance to Niadra, he ran off deeper into the outpost.
He rampaged through the outpost, leaving a trail of bodies in his wake, finally killing the patrons of a bar. Elms hunted him down, and the two exchanged blows before Elms took the flamethrower of a patron and ignited him. Gary shouted that the Swarm would rise again even without her, before he died.