During the United Earth Directorate's siege of the Korhal capital of Augustgrad, Dominion Emperor Arcturus Mengsk attempted to flee the planet in the Dominion flagship Norad III and was intercepted by UED Admiral Gerard DuGalle in the fleet's flagship Aleksander. Before DuGalle could take Mengsk into custody, Jim Raynor arrived in the Hyperion with a small protoss fleet, and warped away with Mengsk.
The UED tracked the two to Aiur, where they had fortified themselves in a protoss base near a functional warp gate. There were also numerous zerg broods in the area, they were currently inactive but might respond to provocation. DuGalle was concerned, but found it a necessary risk, as Mengsk was a considerable threat to the UED's agenda in the sector. The UED deployed their valkyrie frigates to tighten up their air defenses, and the Captain was tasked to engage the protoss and capture Mengsk and Raynor. Vice-admiral Alexei Stukov and Lieutenant Samir Duran were sent to the surrounding area to ensure no external threats interfered with the Captain's mission.
The UED landed a strike team south of the protoss and prepared to move out. However, the warp gate at the protoss base was activated, and its energies triggered the zerg broods to begin attacking protoss and terran alike. The UED's forces fought their way through the zerg and destroyed Raynor's command center, forcing him to flee with Mengsk in a dropship. Before the UED could make plans to intercept them, Stukov detected a massive zerg swarm advancing from the northeast; Duran's position. Stukov contacted Duran to demand an explanation, but Duran said he detected no zerg and that Stukov's signal was faint, and thus cut off the transmission.
An enraged Stukov ordered the Captain to retreat their forces before the zerg overwhelmed them, and told him to tell Admiral DuGalle he would not be returning to the fleet, as Stukov had a personal matter to see to. The zerg descended on the UED, and in the chaos Raynor's dropship escaped to the warp gate and teleported away. The warp gate self-destructed shortly after.
Once the opening attack between AI forces ends, the player receives control of a substantial base. Their approximate provided forces, allowing for losses during the attack, include four siege tanks, seven-five valkyries, two fully upgrades science vessels, six marines, six SCVs, two dropships, and one each of a barracks, engineering bay, factory, and starport. The player should begin by building several supply depots to allow the supply for their new forces, and then an academy so they can upgrade their marines and train medics to support them.
Five minutes into the mission, the warp gate will cause the two zerg broods will become active. The brown zerg will mostly concern themselves with the protoss, while the orange zerg will attack primarily with mutalisks and guardians from the east, which the player's valkyries can handle easily. The primary danger comes from the protoss, who will attack with zealots, dragoons, high templar, and reavers, and have a standing force of scouts and carriers at their base. The player should reinforce their defense with bunkers and more siege tanks as resources allow, and keep SCVs on-hand to repair their bunkers.
The player should expand as soon as they are able; there is a resource node to the north-west guarded by light protoss forces, and another node south-west of the warp gate. Both locations are vulnerable to attack from the brown zerg, who include lurkers in their numbers so the player should keep detection about. The player can use the zerg to their advantage; normally the protoss defenders will easily hold them off, but the player have their science vessels support the zerg with EMP shockwave and defense matrix. While it is unlikely the zerg will be able to do significant damage to the protoss this way, they can possibly destroy the defenders entrenched around the warp gate.
A fleet of battlecruisers will suffice to win the mission, but the player can also opt for a ground force. A squadron of siege tanks and goliaths with support from marines and medics can work, the goliaths focusing their fire on enemy air units, particularly carriers, while the siege tanks destroy reavers and high templar from range and the marines defend them. Whatever strategy the player opts for, the mission is won once they push to Raynor's command center and destroy it.