In the Mass Effect game series, Commander Shepard can shape the future of the galaxy in many ways. In the first game, the fate of the entire Rachni race is in Shepard's hands.
During the Noveria mission, Commander Shepard hunts down Matriarch Benezia and follows her to the reclusive research base of Peak 15. What the Commander finds there is astonishing: A queen of the extinct Rachni race, in the flesh. However, this also presents the Commander with a difficult decision, for which the ramifications will be felt across the entire galaxy for centuries to come.
The Secrets Of The Mu Relay
Commander Shepard arrives on Noveria with a lead: Chasing after Matriarch Benezia, Saren's top minion. She isn't at the Port Hanshan spaceport, however; she has already taken ground transport to the remote Peak 15 research station and by the time Shepard arrives, all ground transport systems are blocked off.
Shepard secures a garage pass and takes the Mako to Peak 15. Soon, the Commander's squad is surrounded by oversized insect aliens, the Rachni. It's time to get some answers.
After fighting through the facility and subduing Matriarch Benezia, Commander Shepard learns there is a Rachni queen alive on Noveria, who happens to hold the key to everything. This Rachni queen has inherited the memories of her mothers and those ancient queens knew the location of the unique Mu Relay. No one else can find that relay, but the Rachnie can. Saren sent Matriarch Benezia to mind-probe this queen and uncover the necessary data.
In fact, the researchers who found the queen's egg aboard a derelict ship were probably unaware of this; they just wanted to grow an army of war beasts. Saren and Benezia both know the Rachni queen can offer something far more valuable, but even after Benezia frees herself of Saren's control and hands over the knowledge of the Mu Relay, there is still a loose end: The queen herself.
A Second Chance
Benezia perishes due to gunshots sustained during the battle, but the queen is alive and well and she's ready to talk. The Rachni are a telepathic hive-mind race and the queen controls a dead Asari commando and speaks through her mouth. Shepard engages in conversation with an alien queen who is not angry, but frightened and desperate.
The aggressive Rachni in this station were born unnaturally and are cut off from their races' normal hive-mind array. They cannot be saved, but the queen herself can. She explains the ancient Rachni war was a mistake and the Rachni are not dangerous or war-mongering people. Instead, they live in peace and they prefer to sing songs of the universe to each other. They are also accomplished engineers.
The Rachni also reproduce rapidly and need a lot of room to live. The other races of the galaxy may react poorly if the Rachni return from the dead and start expanding across the galaxy again. The risk of a second, even more costly Rachni war is possible, but the only alternative is to kill this queen and keep the Rachni in the past. Right now, the queen is inside a modular tank that can either release her, or flood with deadly gas that would destroy her. She cannot decide her fate; Shepard must do it.
In Mass Effect lore, this is one of Commander Shepard's most impactful decisions of all. An entire race's future is on the line and the Paradon option is to believe in the Rachni and allow the queen to go free. If so, she will retreat to unknown space and begin rebuilding her race in peace, unwilling to disturb the other civilizations of the galaxy.
The Renegade route is to take no chances and activate the pod's toxins, killing the queen where she stands. This way, there will definitely not be another Rachni war or galactic tensions with another race entering the stage. It's not an easy decision to make, but it must be made here and now. The Commander looks upon the cornered and frightened queen in her tank and must determine whether this will be the last Rachni queen they ever see.