The missions are available in the Starcraft Demo or downloaded as the precursor campaign, which requires the full version of StarCraft. The demo only includes four missions, including the tutorial, while the downloadable precursor campaign includes two extra missions that fit in between the existing missions.
The multiplayer mode of the demo is very limited, the player is able to play only terran, and has only one map available, "Byways" (2 players, badlands tileset).
The Colonial Magistrate Collins informed the lieutenant that the Sons of Korhal raided Chau Sara, seeking to undermine Confederate authority on outlying worlds. He wished the help of Alpha Squadron to destroy the rebels without involving the local militia. He instructed the lieutenant not to arrest any of the rebels.
The Alpha Squadron forces fended off the Sons of Korhal, but shortly afterwards they made hostile contact with xenomorphs. Collins demanded their immediate destruction, "whatever they are". This minor attack was repelled by the Confederates. Immediately after the encounter with the xenomorphs, an obscure group identifying itself as the Cerberus Recon Squad appeared. They were using advanced technology and claimed they were under orders to oversee the extermination of the xenomorphs and prevent their spread to other colonies. The Cerberus unit dispatched to the scene consisted of two Cerberus Goliaths and four Cerberus Firebats.
Cerberus Commander was very disrespectful of Magistrate Collins. Nonetheless, his forces assisted in the destruction of the local Sons of Korhal base.
Magistrate Collins confirmed to Alpha Squadron that he had known about these xenomorphs for quite some time. They were being studied in the Flannum Installation but contact to the facility had been lost. Now the installation was surrounded by xenomorphs, which had somehow created large, semi-organic structures, some of which were capable of defending themselves. Cerberus Recon Squad and Alpha Squadron cooperated in clearing a path to the installation.
Cerberus said they knew the code for the Flannum Installation (something only Magistrate Collins should have known), which enabled them to use the bio-scanners and confirm the presence of the scientists. However, they were unable to detect the xenomorphs, which had burrowed themselves in the installation floors. During the rescue of the scientists, the xenomorphs displayed some intelligence, setting traps and even staging a counter-assault to prevent the rescue from outside the installation. However, Cerberus was an elite force, and with the support of security guards found hiding within the facility they overcame the xenomorph infestation.
The xenomorphs attacked the city of Los Andares shortly after the rescue of the scientists, and so Alpha Squadron and Cerberus had to rescue the city. Edmund Duke, the commander of Alpha Squadron, personally assisted in the defense of the Los Andares, fighting from his siege tank. Duke and his forces (composed in-game by his tank, four vultures and two SCVs) came to the city when it fell under attack (in-game by zerglings).
During the battles, citizens rioted and were quelled by Los Andares Security.
Alpha Squadron defeated the xenomorph forces in the city.
Afterward, Collins wanted to set up a tight defense against the xenomorphs but the Cerberus commander overruled him, actually taking command of the colony. Cerberus felt now was a good time to attack the primary hive clusters of the xenomorphs. Alpha Squadron and Duke had to go along with this plan. Those xenomorphs were defeated on November 12th, and then Cerberus left with a warning:
"By edict of Confederate High Command, all matters regarding these xenomorphs are under Class 7 Seal. Do not speak of the existence of the xenomorphs or in any way relay the events surrounding their appearance on Chau Sara. Failure to comply with these orders will result in immediate termination. This conversation never took place. We were never here."