Storyline


 * For events from Mass Effect: Ascension onward, see Storyline II.

'''In the year 2148, explorers on Mars discovered the remains of an ancient spacefaring civilization. In the decades that followed, these mysterious artifacts revealed startling new technologies, enabling travel to the furthest stars. The basis for this incredible technology was a force that controlled the very fabric of space and time.'''

They called it the greatest discovery in human history.

'''The civilizations of the galaxy call it... MASS EFFECT.'''

Shanxi and Sidon
The story opens in 2157 with Admiral Jon Grissom, who is on his way to Arcturus aboard the SSV New Delhi to congratulate the graduates of the Alliance's N7 elite training program. Nine years ago, in 2148, scientists discovered a cache of alien technology buried on Mars. These aliens were known as the Protheans, who disappeared for unknown reasons 50,000 years ago. In 2156, an exploration team near the edge of the solar system discovered that Charon, Pluto's moon, was actually a mass relay, a dormant piece of ancient Prothean technology covered by sheets of ice. The Charon Relay granted instant travel across thousands of light-years to another mass relay in a different area of the galaxy. Jon Grissom led a team of brave men and women through the mass relay and became a hero of the Systems Alliance, a global coalition formed after the discovery of the Prothean cache on Mars.

Grissom meets with David Edward Anderson, a promising young graduate of the N7 program, and reports that an unknown alien force has attacked an Alliance post at Shanxi. This begins the conflict later called the First Contact War between the Turian Empire and the Alliance. Several battles ensued until the Citadel Council, a multi-species government devoted to preserving galactic peace and stability, intervened and stopped the conflict. Eight years later, humanity was recognized by the Council and granted an embassy.

In 2165, then-Lieutenant Anderson answers an S.O.S. while patrolling the Skyllian Verge, an isolated region on the farthest fringes of Alliance space. Inside the facility, Anderson and his crew discover an elevator leading to the lower sections of the facility. They are attacked by several mercenaries and discover the dead bodies of the scientists who were stationed there. The evidence suggests they may have been betrayed by one of their own. One remaining mercenary manages to set off a bomb that destroys the entire lower level. Anderson and his crew barely escape with their lives.

On the colony of Elysium, a scientist named Kahlee Sanders, recently stationed at Sidon, has gone AWOL with several classified files. Hearing about the attack while at a bar, she leaves to figure out her next move and is attacked outside by a mercenary posing as an Alliance MP. Kahlee fights him off and, realising her escape from Sidon has put her in danger, runs to find help.

Elsewhere, on Camala, a rich batarian named Edan Had'dah meets with the Blue Suns, an infamous mercenary group in the Skyllian Verge. He hired them to attack the human research facility on Sidon, but they screwed up their attempt to catch Kahlee. He hires a krogan bounty hunter named Skarr to assassinate her.

The Spectre
Anderson arrives at the Citadel, to meet with Ambassador Anita Goyle, the Alliance representative on the Citadel. Ambassador Goyle informs Anderson that the Sidon facility was researching AI. This is illegal under the Citadel Conventions after an incident 300 years ago, when the quarians created an artificial race - the geth - that eventually turned on them. She sends Anderson to locate Kahlee Sanders, who may know who was behind the attack and the whereabouts of Dr. Shu Qian, the brilliant scientist in charge of the Sidon facility.

Meanwhile, the turian Spectre Saren Arterius has tracked an illegal weapons exchange to a warehouse on Juxhi. As a Spectre, Saren is above the law and, unfortunately, bears a grudge towards humanity after losing his brother in the First Contact War. After interrogating one of the arms dealers, Saren learns that the weapons were meant for the Blue Suns, but at the last minute, the organization decided to pursue a different job. Saren's interest is piqued. After hunting a Blue Sun mercenary named Groto Ib-ba, Saren learns about Skarr and his new target.

Tracking Kahlee to Elysium, Anderson is reunited with Jon Grissom, now retired, who turns out to be Kahlee's father. He tells him that he sent her away from Elysium to safety. Anderson leaves but a few hours later, Skarr shows up and attacks Grissom and Kahlee, who was in fact hiding in Grissom's house. Anderson returns and fights Skarr - in the middle of the battle Saren appears and drives Skarr off. However, the krogan manages to escape. Saren questions Kahlee about Sidon. She lies and says they were researching human biotics, knowing that if she revealed the truth about the research being done on Sidon, Saren would alert the Council and the Alliance would be in trouble.

Rescue on Camala
After Saren leaves, Kahlee tells Anderson that all the equipment for the project was supplied by the Dah'tan Manufacturing Company on Camala. They plan to sneak off Elysium and go to the Dah'tan facility. Meanwhile, Skarr returns to Edan who sends him and the Blue Sun mercenaries to destroy the Dah'tan facility and erase any information connecting him to the Sidon facility. Skarr destroys the facility, but Had'dah's contact, Jella, survives and gives Saren Had'dah's name. Meanwhile, news of the AI research at the Sidon facility has reached the Council. When they rebuke Ambassador Goyle, she gets angry, pointing out the prominent role humans have in the galactic arena after such a short time, and negotiates a deal to get the Alliance off lightly with trade sanctions.

Finally able to trust him, Kahlee makes a confession to Anderson. She knows who the traitor was at Sidon - Dr. Qian himself. Anderson is skeptical, but Kahlee explains Dr. Qian was studying something new, an alien artifact that might even pre-date the Protheans. After he started studying it in earnest, Dr. Qian's interest turned into a dangerous obsession. She thinks Dr. Qian is working with Had'dah. Ambassador Goyle tells this to the Council as a show of good faith, and they decide to send Saren after Had'dah - Goyle asks for Anderson to be involved, as a possible Spectre candidate. Meanwhile, Kahlee is to be smuggled off Camala by Alliance marines. But Saren, knowing Had'dah is hunting Kahlee, sees this as a perfect opportunity to lure out the batarian, and leaks word to Had'dah's contacts. Skarr and the Blue Suns ambush the marines, destroy the SSV Iwo Jima, and capture Kahlee to help Dr. Qian's research.

Anderson is furious at Saren, but he needs the Spectre's help to rescue Kahlee, who has been taken to an element zero refinery. Unknown to Anderson, Saren is now more interested in obtaining Dr. Qian's research for himself than saving Kahlee. Saren reluctantly agrees to give Anderson some time to find Kahlee before they blow the building. Anderson sneaks in and kills Skarr, rescuing Kahlee just as Saren destroys the refinery and kills Dr. Qian and Had'dah, stealing Dr. Qian's files.

Returning to the Citadel, Anderson discovers Saren gave a damning report on his conduct during the mission. True or not, it means the Citadel Council is not willing to induct a human Spectre just yet. Without evidence, the Council is not prepared to go chasing after Dr. Qian's 'artifact' either. Despite the attraction between them, Anderson and Kahlee have to part ways. Anderson has his military career to follow, while Kahlee has been promoted and reassigned to a new classified posting.

Meanwhile, Saren has been studying the research he stole, and is fascinated by the description of Sovereign, an enormous starship of devastating power. He believes his whole life, even his career as a Spectre, has just been a prelude to this discovery. Saren plans to use the data to find this warship, and use it to exact his revenge upon humanity.

Mass Effect
The Mass Effect storyline follows Commander Shepard, a human military officer in the Alliance Navy. Born in 2154, Shepard had a difficult early life, but in having to overcome great challenges in the line of duty, the commander has since shown exemplary talent and leadership ability. Currently, Shepard is the executive officer (XO) aboard the SSV Normandy.

Prologue
A prototype Alliance warship, the SSV Normandy, travels from Earth's orbit to the Mass Relay at Charon. On board Captain Anderson is in discussion with Admiral Hackett and Ambassador Donnel Udina concerning Commander Shepard's worthiness to become the first human Spectre, an elite agent for the Citadel Council. Meanwhile, the ship and crew are heading to Eden Prime in the Utopia system for their shakedown mission.

Shepard heads to the bridge where Joker, the pilot, guides the ship into the Mass Relay. Because of the presence of Nihlus Kryik, a turian Spectre sent by the Council to observe, and the famed Captain Anderson, several members of the crew think their true purpose at Eden Prime is far more important than a simple shakedown run. After making the jump, Captain Anderson asks Shepard to come to the comm room for a briefing. Nihlus has time to speak to Shepard before Anderson joins them. Together they inform the commander that a Prothean Beacon has been discovered on Eden Prime. Prothean technology has immense scientific value, but since Eden Prime is close to the Terminus Systems, the beacon is at risk from pirates and mercenary bands. This is the Normandy's true objective: recover the beacon. This mission will also be Nihlus' chance to observe Shepard in action, the first of several they will undertake together to assess Shepard's candidacy for the Spectres.

The briefing is interrupted by a transmission from Eden Prime that Joker patches through. The footage shows Alliance soldiers fighting on the surface, under heavy fire and requesting reinforcements. As Shepard, Anderson and Nihlus watch, they see a huge dreadnought hanging over the surface. Anderson orders Shepard to get ready - this is going to be worse than they thought.

Eden Prime
As the Normandy touches down on Eden Prime, Cpl. Richard L. Jenkins, Lt. Kaidan Alenko and Commander Shepard prepare to head down to the planet. Nihlus is going groundside too, but goes on ahead. In the first few minutes on the surface, geth assault drones appear without warning and cut down Jenkins. Shepard and Alenko continue towards the dig site, discovering the only surviving marine, Gunnery Chief Ashley Williams, who is being chased by geth troopers. Shepard and Alenko help her fight them off. Williams can't explain why the geth are here, but they've wiped out her whole unit.

Williams leads them to the dig site but the beacon has been moved to the spaceport. While they examine the nearby camp, the squad run into a group of Husks, human corpses reanimated by the geth, which they manage to kill. Shaken, they continue towards the spaceport where Nihlus agreed to meet with them. Meanwhile, Nihlus is surprised to see Saren Arterius, a fellow Spectre, at the train platform. Saren tells Nihlus he's got everything under control, but when Nihlus turns his back, Saren kills him and leaves, ordering the geth to destroy the colony with explosives. He approaches the Prothean Beacon, which reacts by lifting him off the ground.

After finding Nihlus's body, Shepard's team continues to the tram area where they defeat the last of the geth and disarm their demolition charges. Shepard sees the beacon and calls the Normandy while Alenko and Williams take a look at it. One of them gets too close and is caught in some sort of field - Shepard intervenes but is caught in the field instead, pulled off the ground as Saren was. The commander suffers a horrific vision - synthetics waging a terrible war - before the beacon explodes and Shepard is thrown to the ground, unconscious.

Full walkthrough — Detailed plot summary

The Citadel
Aboard a huge dreadnought, Saren is given a report by an asari matriarch. The news isn't good - Eden Prime has been saved by Captain Anderson's crew, and one of them may have used the beacon. Saren flies into a rage but restrains himself from attacking her, ordering that this human must be eliminated.

Fifteen hours after the Eden Prime attack, Shepard wakes up in the Normandy's medical unit, much to the relief of Alenko and Williams. Doctor Chakwas says the commander is physically okay, but has increased REM and unusual beta waves. Shepard mentions the vision but can't explain it. Captain Anderson briefs Shepard about Saren. He is a powerful and legendary Spectre but also outspoken against humans. If Saren is in charge of the geth, that means he has gone rogue, and they must tell the Council. Upon arriving at the Citadel, Ambassador Udina tries to convince the Council to remove Saren's rights as a Spectre, but only succeeds in getting an audience. Shepard, along with Alenko and Williams, continues to the Citadel Tower and meets Garrus Vakarian, a turian C-Sec (Citadel Security) officer investigating the charges against Saren. He hasn't found anything useful: Saren's Spectre status makes him untouchable.

The Council audience doesn't go well. The Alliance has little evidence and Saren - viewing the proceedings from a hologram - openly laughs at Shepard's vision. They need more to go on. Garrus, the C-Sec officer, might be able to help. Udina tells Shepard to find Harkin, a retired C-sec officer who could help them find Garrus. Anderson also suggests speaking to Barla Von, a financial expert on the Citadel who works for the Shadow Broker. When Shepard hears Garrus was last seen in the Med Clinic, the commander intercepts a couple of thugs threatening Dr. Chloe Michel, and saves her with Garrus' help. From the two of them, Shepard learns that a quarian has recently arrived on the Citadel, claiming to have evidence of Saren's connection to the geth. However this quarian is being held captive by Fist, a local crime lord who used to work for the Shadow Broker, but who's now betrayed the Broker to work for Saren.

Along with Garrus, the group gains the aid of Urdnot Wrex, a Krogan Battlemaster, mercenary and bounty hunter who has been paid by the Shadow Broker to kill Fist. They raid Chora's Den and discover the quarian was supposed to hand the information over to the Shadow Broker, but this meeting is a trap. Saren's men will be the ones waiting. Shepard races to the meeting and manages to save the quarian, Tali'Zorah nar Rayya. They bring Tali back to the Ambassador's offices.

The evidence she found was an audio file she managed to save from a geth, which has clear evidence Saren was behind the attack on Eden Prime. However, the file also hints that Saren is looking for something called the Conduit with the aid of a powerful asari called Matriarch Benezia, to bring about the 'return of the Reapers'. The Council aren't interested in the Reapers, but they can't ignore this evidence and strip Saren of his Spectre status.

As people in the Chambers watch in amazement, Commander Shepard becomes the first human Spectre and is tasked with hunting Saren down. Captain Anderson steps down as commander of the Normandy and hands the ship over to Shepard, along with some useful leads. There have been reports of geth activity on the planets Noveria and Feros. Also, Matriarch Benezia, Saren's ally, has a daughter named Dr. Liara T'Soni, a Prothean expert who may have useful information. After giving the crew a speech, Shepard is now in command of the Normandy.

[Note that the next three missions can be done at any time, and therefore some dialog or events may change according to the order you perform the missions in.]

Full walkthrough

Liara
The Normandy tracks Liara T'Soni to Therum, a mining colony in the Knossos system of the Artemis Tau cluster, but the geth are already on the surface, taking over several refinery facilities and dropping Geth Armatures from overhead.

Shepard leads the squad to a mineshaft and down into a Prothean ruin, where they find Liara trapped behind a Prothean barrier curtain. Freeing her, they discover she is not in league with Saren and has no idea what the Conduit might be. As the squad leaves the ruined tower with Liara, they are confronted by a krogan battlemaster who is leading the geth and manage to defeat him as the unstable ruins begin to collapse. They escape just in time.

During the debrief, Liara explains her expertise is on the Prothean extinction. She has a theory they were not the first civilization to mysteriously vanish, and is amazed by Shepard's story of the Reapers.

Full walkthrough — Detailed plot summary

Noveria
Shepard arrives at Noveria and discovers that Matriarch Benezia recently arrived. She and Saren are investors in Binary Helix, which has a lab up on Peak 15. Benezia has gone there on business. However the lab has since issued a Code Omega signal, meaning there are critical problems, and a blizzard has cut off shuttle access. After wrangling with Administrator Anoleis, Shepard manages to get a garage pass and drives up to Peak 15.

The facility is deserted save for geth and bizarre creatures - the rachni - which have escaped from the labs. Shepard reactivates the station's VI, Mira, and goes up to Rift Station looking for Benezia. Rift Station is full of science staff sheltering from the rachni attack; Shepard can help them out but gets attacked by those loyal to Benezia. The squad discovers Binary Helix discovered a rachni egg that turned out to be a queen, and were trying to breed an army from her brood until the rachni turned on them.

Down in the labs through the maintenance area, Shepard finds Benezia with the Rachni Queen. The matriarch attacks the squad, but after a fierce battle Benezia manages to overcome the indoctrination that Saren has used to control her, and tells Shepard the truth. Saren wants the location of the lost Mu Relay, and sent her to retrieve it from the queen's genetic memory. Benezia doesn't know what else he is planning. She hands the coordinates over to Shepard, but becomes lost to the indoctrination again and the commander has to kill her. After deciding what to do with the Rachni Queen, Shepard leaves Noveria with Benezia's data and another piece of the puzzle.

Full walkthrough — Detailed plot summary

Feros
Drawn to Feros by rogue geth activity, Shepard and the squad arrive at the Zhu's Hope colony, owned by ExoGeni Corporation. The colony has been suffering repeated geth attacks and the settlers there are acting strangely. Shepard clears the geth for the colonists and takes a Mako along the Prothean Skyway to the main geth base. The squad finds a small group of colonists who have become separated from the others, led by Juliana Baynham and a nervous ExoGeni rep, Ethan Jeong. Despite their situation these survivors seem to be coping better than Zhu's Hope. Before they leave, Juliana asks Shepard to look for her daughter Lizbeth, whom she believes to be still inside ExoGeni Headquarters.

After making their way inside the ExoGeni Headquarters, Shepard's squad finds Lizbeth, scared but alive. From the company VI, Shepard discovers that the corporation has been experimenting with a mind-controlling plant, the Thorian, and that Zhu's Hope is actually a testing ground for ExoGeni to study its abilities. Shepard disables the force fields that the geth have set up by knocking the geth dropship off the headquarters and returns to the Skyway group. Jeong has received word that ExoGeni wants Zhu's Hope destroyed. Shepard deals with Jeong and heads back to Zhu's Hope to find the Thorian.

Controlled by the Thorian, the colonists attack Shepard on sight. Some have been turned into Thorian Creepers. Shepard can use special gas grenades that instantly kill the creepers and harmlessly paralyse the colonists, then descends beneath Zhu's Hope to find the Thorian. It is an enormous creature that looks nothing like a plant. It creates an asari clone to speak for it, but only to tell Shepard it's not interested in bargaining with 'meat'. After battling waves of Thorian Creepers and clones, Shepard manages to destroy the Thorian's neural nodes and kill it.

An asari emerges from a Thorian pod, and manages to explain what happened. Shepard learns that Saren sacrificed this asari ally, Shiala, to the Thorian to gain the Cipher. This is the cultural and ancestral experience of the Protheans, which is necessary to understand the vision that the Eden Prime beacon put into Shepard's mind. Freed from the Thorian, Shiala transfers the Cipher to Shepard. With it, once Shepard has had time to adjust, the vision will make more sense and hopefully lead them to the Conduit before Saren.

Full walkthrough — Detailed plot summary

Virmire
The Council contacts Shepard with a possible lead. A salarian espionage team on Virmire, investigating reports of Saren's activities, has sent a mission-critical transmission that was almost lost in static. Shepard heads to Virmire and meets the leader of the salarians, Captain Kirrahe. They have found a breeding facility for krogan that Saren is using to create an army.

Kirrahe, realising he's not getting the reinforcements he needs, asks for Shepard's help destroying it and they develop a plan. While the salarians distract Saren's geth, Shepard will take a team around the back and plant a nuclear device that will wipe out the facility. Kirrahe asks Shepard for a squad member to help him coordinate the attack - Shepard can send Ashley or Kaidan to help the salarians, but must also deal with Wrex, who is furious that Shepard is willing to destroy a cure for his people's genophage.

Leading the strike team, Shepard reaches the facility, but discovers its main purpose is not to breed krogan, but to study Sovereign's horrific indoctrination effect. In Saren's private lab the team finds another Prothean Beacon that gives Shepard another vision, and they are confronted by a hologram of Sovereign itself, which is not a Reaper ship but an actual Reaper.

Shepard manages to get the nuke set up across the facility only to get a call that the salarians are being attacked with heavy losses. The commander takes a group to help them but as they leave, the geth start attacking the nuke site and Shepard has to choose: both Kaidan and Ashley are in trouble and there's no time to save both. Once the choice has been made Shepard brings reinforcements in, only to be confronted by Saren. He tries to make the commander join his cause but Shepard refuses, fighting Saren off. Saren gets away and the team board the Normandy, escaping Virmire as the nuke destroys the facility.

Full walkthrough — Detailed plot summary

Mutiny on the Normandy
Thanks to the undamaged beacon on Virmire, Shepard's Prothean vision is now complete. During the debrief, Liara touches Shepard's mind to interpret it fully. The vision was a distress call intended to warn the Protheans about the Reapers. Liara realises that the landmarks in the vision are on Ilos, a planet she has studied as part of her Prothean research. Ilos had been impossible to reach because it was only accessible through the Mu Relay, which is why Saren needed the Relay's location from Noveria. After the debrief, Joker has a message for Shepard from the Council: they're putting together a massive multi-species effort to face Saren.

Thrilled the Council are finally taking this seriously, Shepard returns to the Citadel, wanting to personally lead the assault. But once back at the station, Shepard discovers the Council are only putting up a blockade around the Mass Relays to stop Saren reaching the Citadel. Neither they nor Ambassador Udina believe Shepard's story about the Reapers and they refuse to send a fleet to Ilos. The Mu Relay is in the Terminus Systems and a Citadel fleet there could start a war. Shepard knows the Normandy's stealth systems can get them there discreetly, but the Council are getting tired of Shepard's insistence that the Reapers are the real threat. Udina, wanting to make nice with the Council, locks out the Normandy's systems and grounds the ship.

Frustrated, knowing Saren is close to finding the Conduit and they're losing time, Shepard is grateful when one of the squad offers support, but a real breakthrough comes when Captain Anderson gets in touch, asking Shepard for a discreet meeting at Flux. Anderson believes the commander's story and knows the Normandy is the only ship that can get Shepard to Ilos. He is going to unlock the Normandy's systems, allowing Shepard to steal the ship and take her to Ilos. Shepard is concerned that Anderson will be arrested and charged with treason - or worse - but Anderson sees his future as a small price to pay for stopping a galactic menace. Shepard goes to the Normandy and waits with Joker on the bridge. With Anderson's help the Normandy's systems are unlocked and they escape the Citadel, heading to Ilos.

Ilos
After Shepard's love interest 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 that must be Saren, but there's no landing zone nearby. Shepard suggests dropping the Mako, but they need about 100m of open terrain for a safe drop and Pressly can only find 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.

Shepard looks for some way to override it. After fighting through the geth left on guard, Shepard and the squad find a security station and open 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.

The Citadel is a trap, actually 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. Sovereign is the vanguard of the Reapers. After every Reaper attack, they leave behind one of their kind to survey and gather information on what the civilizations are up to. Once the galaxy's races have advanced enough, Sovereign will activate the Citadel Relay and usher in the next genocide. The reason the Reapers harvest the galaxy of all organic life 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 wiped clean, the Reapers return to dark space to hibernate and save energy. In this state, they are apparently vulnerable, so they always seal the Citadel Relay behind them.

When the Reapers attacked 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 'contingency planning', and shut off the pods of non-essential personnel to conserve energy, hoping that when the time was right, he could at least open some of the pods. Vigil managed to save a dozen scientists.

The Conduit was a small prototype mass relay, built by the Protheans, designed to transport personnel from the research center on Ilos to the Citadel, but only in one direction. (The 'Mass Relay Statue' in the Presidium is actually a working mass relay connected to the one at Ilos). After the Prothean extinction, the few remaining Protheans on Ilos traveled to the Citadel through the Conduit, and reprogrammed it so that the keepers would not respond to the signal to activate the relay to dark space. Sovereign needed to find another way of activating the Citadel Relay, and it used Saren to find it. Saren will go through the Conduit, and gain control of the Citadel from the inside. Meanwhile, Sovereign will head to the Citadel. Once Saren transfers control of the station, Sovereign can open the Citadel Relay manually. Vigil explains that Reapers are patient. If Sovereign assaulted the Citadel alone, the combined power of the Citadel Fleet could be enough to defeat the Reaper. But with someone going in the back door to give it control, Sovereign will be able to usher in the next Reaper invasion, and complete its mission. Sovereign has been planning this for centuries, after discovering the Protheans used the keepers to try to break the cycle.

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. It is a small mass relay pointing straight up, connected to the Citadel. Saren has already gone through and left more geth on 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 and drives the Mako directly at it. Just before the relay closes, the Conduit jumps the Mako through to the Citadel.

On the Presidium, now burning and heavily damaged, two geth troopers become curious about the strange blue glow around the Relay Monument. When they go to take a look, the Mako suddenly bursts through and crushes them, before rolling over and crashing against a wall. The race to stop Saren is on.

Full walkthrough — Detailed plot summary

Siege of the Citadel
Shepard and the team manage to get out of the overturned Mako and use the nearby malfunctioning Avina terminal to get a sit rep. Saren is heading toward the Council Chambers and the whole station is infested with geth. The squad tries taking the elevator to the Citadel Tower, but it stops halfway when Saren locks down the station's systems. Shepard tells the team to suit up and blows out the elevator's glass with a shot. They have to walk the rest of the way in zero gravity with their boots magnetized.

Meanwhile up in the Chambers, Saren - angrily shooting keepers as he goes - reaches the central console and uses it to take control of the Citadel. As Sovereign gets closer, crushing the Citadel Fleet ships in its path, Saren closes the Wards, creating an impenetrable shell around the Reaper and the geth dropships already inside. Sovereign settles on top of the Citadel Tower, preparing to open the Citadel Relay once Saren transfers full control.

Elsewhere Shepard and the team are fighting for their lives against the geth and Saren's krogan warriors out on the Citadel's exhaust plains, trying to get to the Chambers. A geth dropship appears and starts unleashing shock troopers on them; Shepard activates the Citadel's defense turrets, and with their cover fire, takes the dropship out. Further along they run into several powerful geth turrets and have to use cover to get close enough to destroy them, or manage to sneak down a side route where krogan battlemasters are waiting. Eventually they reach a maintenance hatch that leads down into the Council Chambers, now burning and full of Saren's geth. The stairways provide some cover as the team fights towards the central console.

At that moment Saren appears and throws a grenade. Shepard's team are blown aside while the commander takes cover close to Saren. He urges Shepard not to be a fool - everything is lost if Shepard continues resisting Sovereign. Saren boasts that his faith faltered but Sovereign has implanted him, made him partly synthetic, perfect. This is the future of organic life. Shepard can't believe Saren allowed Sovereign to implant him. Shepard can attack Saren straight away, or try talking him down - the more Shepard talks, the more Saren is convinced, but his Reaper implants cause the turian intense pain when he begins to agree with Shepard. With enough convincing, Saren thanks the commander for freeing him before shooting himself in the head. In either case, he falls to the bottom of the Chambers, falling through the glass floor and being impaled by a large shard.

Using the central console, Shepard uploads Vigil's program and gains control of the Citadel. With advice from the team, Shepard opens a communication channel and gets Joker... who has the Fifth Fleet just waiting for the commander's word once the mass relays are unlocked. Shepard has to decide between sending the Fleet to defend the Destiny Ascension and save the Council, letting the Council die, or focusing on Sovereign. Once the orders are given, Joker brings the Fleet through the nearby mass relay as Shepard opens the Citadel's ward arms.

As the Fleet engages the ships outside - geth dropships and Sovereign itself - Shepard tells the squad to check Saren and make sure he's dead. They drop down to the bottom of the Chambers - one coldly shoots Saren in the head, while the other confirms the kill to Shepard. Suddenly Saren's body begins to twitch as his implants fire up, burning his flesh away until he is a cybernetic construct like a Husk, completely possessed by Sovereign. The shockwaves from his transformation cause the platform to collapse and Shepard falls into the bottom of the Chambers. The squad fights back against the creature, but it is fast and deadly.

Outside, the Normandy is leading the attack against Sovereign. The Reaper unleashes a terrible weapon that burns through several Alliance ships, but the Fleet is slowly getting the upper hand. As the squad finally destroy the cybernetic creature and it burns away to ashes, Sovereign begins to weaken under the Alliance attack and releases its grip on the station. A blast from the Normandy is the coup de grace and the Reaper is destroyed.

In the Chambers, Shepard looks up to see a huge piece of debris from the Reaper heading straight for the Tower. The commander yells for the squad to take cover, just as it hits.

Much later, rescuers enter the Tower looking for survivors. Under a pile of rubble they discover Shepard's team... two of them, badly wounded but alive. Leading the rescuers, Captain Anderson helps them out, assures them that it's all right, and asks where Commander Shepard is. One of the squad looks sadly across the Chambers, where the Reaper debris has crashed into the floor. It would have crushed anyone standing under it. The rescue team help the squad out of the Chambers, and Anderson looks back - to see someone moving. Commander Shepard, with an injured arm, manages to climb out from behind the debris, limps toward them, and smiles.

Full walkthrough

Epilogue
As a result of Shepard's decisions, there are three outcomes to the story:


 * The Council is destroyed and the Alliance forms a new Council, with no other races involved. Shepard can nominate either Ambassador Udina or Captain Anderson to chair the new Council, and they prepare to combat the Reapers with the Alliance Fleet at the forefront.
 * The Council is destroyed and the Alliance forms a new Council, with a human chairman but the other races remaining on the Council. Shepard can nominate either Udina or Anderson to chair the new Council, and they prepare to combat the Reapers with the Alliance Fleet at the forefront.
 * The Alliance Fleet saves the Council. In gratitude for the sacrifices of the Alliance Fleet and Shepard's help, they offer humanity the chance to become a Council race. Again, Shepard can nominate either Udina or Anderson to be the human representative, and they decide to unite all the Citadel races against the coming threat of the Reapers.

In all three endings Shepard leaves the Citadel aboard the Normandy, intending to find a way to stop the Reaper invasion.

Continue to Storyline II →