UNC: Besieged Base

You'll receive this mission from Admiral Hackett, who sends you to the planet Chohe, in the Cacus System of the Hades Gamma Cluster in order to eliminate a group of biotics who have besieged a medical base.

While the biotics themselves are not a particularly difficult fight (they seem to use their powers less frequently than their ilk), the mission is complicated by the presence of addled scientists who will wander into the line of fire and who it is your job to save. Accidentally (or deliberately) killing the scientists will give you different ending messages.

Return to the Normandy and use the Galaxy Map to talk to Hackett and end the quest.