Ilos



Shepard and Liara.

After Liara spends a night in the Commander's quarters, Joker announces that they're about to pass through the Mu Relay, and they soon arrive at Ilos. Shepard sees that Saren has already arrived with a fleet of geth dropships, though the Normandy's stealth system is keeping them safe for now. Navigator Pressly picks up some readings on the planet confirming Saren's presence. However, they can not find a landing zone. Shepard suggests dropping the Mako but they need about 100m of open terrain for a safe drop and Pressly can only find at most 20m. Joker insists that he can do it. The Mako is successfully dropped outside an ancient bunker, but Saren and his geth have already made it inside, shutting a heavy security door behind them.

　

Vigil, the Prothean VI.

Shepard looks for ways to get to the other side of the bunker doors. After fighting through the geth left on guard, Shepard and the squad find a security station and reopen the bunker doors. While in the control room, Shepard discovers an ancient Prothean recording which is heavily damaged. The Cipher allows Shepard to make out some of the words—it's another warning about the Reapers but it's just too broken up. They return to the Mako and enter the bunker. After driving past cryogenic stasis pods, all apparently shut down, Shepard sees a mysterious energy barrier. As the Mako reaches the barrier, another barrier appears behind them, trapping the squad inside. The only way out is through a door at the side of the wall. After heading down an elevator, Shepard finds an ancient Prothean VI named Vigil, who has information Shepard needs to stop the Reapers.

A keeper at work.

Vigil unveils a startling revelation. The Citadel is actually a trap; a huge mass relay linking to dark space, outside of the galaxy, where the Reapers are waiting. The keepers are presumed to be one of the earliest races to be indoctrinated by the Reapers, who set them the task of maintaining the Citadel and activating the Citadel Relay when Sovereign signals them. It is also revealed that Sovereign is the vanguard of the Reapers. After every Reaper attack, they leave behind one of their kind to act as a vanguard and to monitor the development of the galaxy's races. Once the galaxy's races are sufficiently advanced, the vanguard will activate the Citadel Relay and usher in the next genocide. The reason the Reapers harvest the galaxy of all advance organic life approximately every 50,000 years is currently unknown. According to Vigil, not even the Prothean scientists could comprehend why they do it. They may be driven by goals that organics find impossible to understand. Once the galaxy is harvested, the Reapers return to dark space to hibernate and conserve energy. In this state, they are apparently vulnerable, so they always seal the Citadel Relay behind them.

The Relay Monument.

When the Reapers last attacked about 50,000 years ago, their genocide of the Protheans lasted for centuries. Ilos' personnel hid in cryogenic stasis, watched over by Vigil. However, as his energy reserves ran low, he followed a contingency plan by shutting off pods of non-essential personnel to conserve energy, hoping that when the time was right, he could safely open the pods. In the end, Vigil managed to save a dozen scientists. The few remaining Protheans on Ilos traveled to the Citadel through the Conduit—a small prototype mass relay, built by the Protheans, enabling a one-way link from Ilos to the Relay Monument in Citadel Presidium. The survivors altered the signal that the keepers respond to and prevented them from activating the relay to dark space.

Vigil also explains that if Sovereign assaults the Citadel alone, the combined power of the Citadel Fleet would be enough to defeat the single Reaper. However, if Sovereign is able to direct an agent to go through the Conduit as a back door and transfer control of the Citadel back to Sovereign, it will be able to manually activate the Citadel Relay and bring in the rest of the Reapers. Sovereign had possibly planned this for centuries after discovering the Protheans' sabotage plan.

The Conduit on Ilos.

Vigil gives Shepard a data file that will give the commander temporary control of the Citadel to stop Sovereign. After leaving Vigil, Shepard heads through the archives, down into an old aqueduct guarded by geth, and reaches the Conduit. Saren had already gone through, leaving geth to stay guard.

Meanwhile, Sovereign begins its assault on the Citadel, escorted by a large geth fleet. The commander of the Destiny Ascension attempts to close the Citadel but the station doesn't respond—the operators at Citadel Control are all dead. Saren has begun his attack from within.

Back on Ilos, Shepard sees the Conduit is closing fast. Rushing to the Conduit, Shepard evades the geth in the process and drives the Mako through, just before the relay closes.