|Ruins of Tarsonis|
Following the defeat of General Edmund Duke at Dylar IV, the UED Expeditionary Fleet commandeered a number of battlecruisers and pressed most of the surviving Terran Dominion defenders stationed on the planet into their service. As the UED prepared to move on to their invasion of Korhal, vice-admiral Alexei Stukov reported the UED's scouts had found a mysterious weapons relay on Tarsonis, called the psi disruptor.
Lieutenant Samir Duran debriefed the UED commanders on the significance of the device. During the reign of the Terran Confederacy, they developed the psi-emitter, which had the ability to lure zerg to their signals. The Confederates were rumored to be developing a specialized emitter that could disrupt zerg communications, but Arcturus Mengsk never found it. Duran believed the psi disruptor was the rumored Confederate weapon, and suggested it be destroyed, lest it fall into the hands of the Dominion.
Admiral Gerard DuGalle agreed with Duran, but Stukov protested the device could be critical to the defeat of the zerg. Duran questioned Stukov's faith in the UED, and assured him they would not need the device to prevail. The two began to argue and were halted by DuGalle, who reasoned that, with the UED's eventual goal of taking control of the zerg, the psi disruptor could be used against them. He ordered the UED to set course for Tarsonis.
On Tarsonis, DuGalle sent Duran to destroy the disruptor with a small strike team. Once on the surface, however, the UED picked up massive numbers of zerg in the area. Duran and the Captain focused on destroying the zerg hives, which disrupted the zerg enough that they could no longer operation. With the zerg pacified, Duran reached the psi disruptor and prepared to plant explosives on it. Then, members of Stukov's Elite Guard approached and relived Duran, telling him they were there to see to the disruptor's disassembly on ordered from Stukov. Duran acquiesced to their authority and returned to the Aleksander.
Unbeknownst to Duran, DuGalle, or the Captain, Stukov's men did not destroy the disruptor; on Stukov's orders, the psi disruptor was transported to Braxis and reassembled, as Stukov believed the disruptor was too great an advantage to throw away.
The player is surrounded by four different zerg forces and will be vulnerable to attack from multiple directions. They must establish bunkers and siege tanks for defense as soon as their economy allows. The player is able to destroy the hives in any order, but each hive demands its own strategy due to the composition of its forces and the layout of the base.
The hive to the east of the player's base is vulnerable to attack from the high ground, so the player should in a force of siege tanks, at least six, and use their siege mode to bombard the hive. The zerg will retaliate with zerglings, hydralisks, and mutalisks, so the player should have a force ready to defend them; marines, firebats, and medics will suffice. When the hive is destroyed the brood goes inactive for the rest of the mission.
With the first hive destroyed the player can securely expand to the southern mineral field, and can also destroy the zerg hive itself and expand there if they wish. The hive to the north-west is inaccessible by land, but the player can use this to their advantage. The player should build two starports and begin building wraiths. With the same force that just destroyed the last hive, the player can move their siege tanks to the cliff south of the next hive and use wraiths to spot the high ground for them. Resistance will be limited to mutalisks, since the ground forces cannot reach the siege tanks, and the player can fell the hive easily.
The northern hives are much more specialized. The north-west hive has many sunken colonies and ultralisks, but few air defenses. A team of wraiths should be dispatched to the hive to destroy it; the small number of hydralisks they will encounter are easily killed. The north-east hive is full of colonies with mutalisks and guardians. A team of marines with medic support and goliaths with the charon booster upgrade can sweep through the base and destroy the hive.
A dummied out trigger in the map contains a response from DuGalle when Duran suggests destroying the hives; DuGalle orders the Captain (the player) to aid Duran in this, while DuGalle and the rest of the fleet move forward to Korhal. This is the given reason why the player is unable to build battlecruisers in this mission.