Mass Effect 3 - Synopsis - Plot

Plot

Mass Effect 3 begins on Earth with Commander Shepard having been detained following the events in Arrival. In the opening moments it is revealed that Earth has recently lost contact with its extra-solar assets and is hastily preparing for the imminent Reaper arrival. The assault comes moments later, and all of Earth's defenses are overwhelmed. Shepard escapes a burning Vancouver on the Normandy with the help of Admiral Anderson and either Kaidan Alenko or Ashley Williams (depending on which survived Virmire) and leaves to gather help from other species while Anderson coordinates human resistance on Earth. Before leaving the Sol System, Shepard is ordered to Mars by Admiral Hackett who claims that researchers have uncovered something that may give humanity a chance against the Reapers. There, Shepard battles Cerberus forces and encounters former squad-mate Liara T'Soni, who has discovered plans for a Prothean superweapon that may be capable of defeating the Reapers. Before leaving the facility, Shepard speaks with a now-hostile Illusive Man, who claims he wants to use the Prothean weapon to take control of the Reapers. Shepard pleads for help from the Council, but they are reluctant to oblige due to their own preoccupations and unwilling to bet everything on an untested device. Shepard realizes that the only way to gain other species' assistance will be to help them in their own wars against the Reapers and garner favors, while at the same time gathering war assets to be used against the Reapers in battle. Eventually, Hackett begins construction on the Prothean weapon and dubs it "The Crucible".

After rescuing the turian primarch from a battle on one of Palaven's moons (as well as reuniting with squadmate Garrus Vakarian), Shepard convenes a war summit, consisting of himself, the primarch, and representatives for the salarians and the krogan. The primarch promises Shepard turian support for Earth, but only if the krogan agree to help defend Palaven. The summit goes badly at first, with Urdnot Wrex/Wreav (depending on whether Wrex survived Virmire) withholding all krogan support until a cure for the genophage can be created. The cure is being developed on the salarian homeworld of Sur'Kesh by former squadmate Mordin Solus (if he survived the events of Mass Effect 2) and a team of scientists. After a series of battles on Tuchanka, the krogan homeworld, Shepard can either cure the genophage or trick Wrex/Wreav into believing it has been cured. If Shepard decides to go forward with the cure, Mordin sacrifices his life at the last moment to counteract a salarian-planned sabotage to it. If Shepard decides not to use the cure, he is forced to shoot Mordin to prevent him from fixing the sabotage unless he can convince him that it would be best to leave the genophage uncured.

After gaining the support of the krogan and the turians, Shepard learns that Cerberus has launched an assault on the Citadel. While there, he deduces that human Councilor Udina is behind the attack and kills him, saving the rest of the council. Shepard also encounters Kai Leng, a notorious Cerberus assassin, and drives him off with the help of Thane Krios (if he survived the previous game).

Shepard then travels to the Far Rim to meet with the admirals of the quarian flotilla. He learns that the quarians have gone to war with the geth, and are attempting to reclaim Rannoch, their homeworld. With Tali'Zorah nar Rayya, Shepard boards a geth dreadnought that is broadcasting a short-range Reaper code to the geth. He destroys it and finds Legion (or an identical geth VI, also dependent on the suicide mission), who tells Shepard that the geth, losing the war with the quarians, turned to the Reapers in desperation and were greatly enhanced at the cost of their independent thought, while Legion/the geth VI remains independent due to its unusual amount of active programs. With Legion/the geth VI's help, the geth are pushed back to a Reaper base which is projecting another Reaper signal. The source of the signal is discovered to be an actual Reaper, and with the help of an orbital strike from the quarian fleet, Shepard destroys it. With the Reaper control gone but the superior upgrades still viable, Shepard must choose either to allow the geth to upgrade and become fully individualized and free, in which case they retaliate against the quarian flotilla, annihilating it and causing Tali to commit suicide, or to shut down the geth consensus, which in turn allows the quarians to destroy the geth fleet and end them as a race. Alternatively, depending on past decisions, Shepard can allow the geth to upgrade while convincing the quarians that the geth do not want to fight them, making peace between the two and gaining support for Earth from both.

Shepard is then informed by the asari councilor of a Prothean artifact on the asari homeworld, Thessia, which may be the key to finishing the Crucible. However, when the Normandy arrives on Thessia, the planet is already under heavy Reaper attack. Shepard must defend Thessia while simultaneously gathering information on the "Catalyst", an essential tool for the Crucible's effectiveness. The artifact the asari councilor referred to is revealed to be a Prothean beacon housing a VI called Vendetta. As it is about to reveal information regarding the Catalyst, Kai Leng arrives and steals the VI program. Deciding to take the fight to the Illusive Man, Shepard follows Leng to the Sanctuary research facility on the human colony Horizon, which Cerberus has been using to research methods of controlling the Reapers. There, Shepard saves Miranda Lawson (or her sister, if Miranda is dead) from her father and Leng in the research facility. Either of the sisters gives Shepard the location of Cerberus headquarters, which, with the help of Admiral Hackett and an Alliance fleet, Shepard assaults, killing Leng in the process but failing to capture the Illusive Man. After reacquiring Vendetta, Shepard learns that the Citadel itself is in fact the Catalyst and that the Illusive Man has now become fully indoctrinated by the Reapers. Because of his indoctrination, the Illusive Man has informed the Reapers of the Citadel's pivotal function in the activation of the Crucible. In response, the Reapers capture the Citadel and move it to a defensible position above Earth, massing their fleets around it.

Under Hackett and Shepard's leadership, the combined fleets of all the races of the galaxy launch a massive final attack on the Reaper forces above Earth and on its surface in a last-ditch attempt to retake the Citadel and use it to activate the Crucible. After landing, Shepard assists in an assault on London, at the center of which there is a beam that connects to the orbiting Citadel. Reunited with Anderson, Shepard eventually begins the final push to the Citadel beam, but the attack force is decimated by Harbinger, the oldest and most powerful of the Reapers. During the charge, Shepard's squadmates are injured and evacuated. Shepard continues the charge alone, but is severely wounded in a blast from Harbinger, barely making it to the beam. Once on the Citadel, Shepard hears from Anderson, who also made it to the beam. Finding Anderson under the influence of the Illusive Man, Shepard succeeds in stopping the Cerberus leader, but Anderson is fatally wounded in the process. After opening the Citadel arms so that the Crucible can dock, Shepard is transported to the pinnacle of the Citadel where a childlike AI appears. The AI declares that it is the Catalyst, and the creator of the Reapers. It reveals that the Reaper cycle is an attempt to prevent organic life from destroying itself by creating synthetic life; creators, the Catalyst argues, are always doomed to be destroyed by the created. The Catalyst characterizes the harvest as an ascendance, wherein advanced organic races are preserved in Reaper form and the opportunity is created for more primitive species to rise, evolve, and advance. In every cycle, the Catalyst studies the evolution of these organic species as well as their technological progression with the ultimate goal of finding a solution to the conflict between synthetic and organic life.

The Catalyst says that it has lost faith in the Reapers' ability to achieve this purpose and gives Shepard three options of defeating them: control the Reapers, destroy the Reapers and all synthetic life, or synthesize all organic and synthetic life. Each choice results in Shepard's apparent death and the destruction of the entire mass relay network. London suffers varying degrees of damage and the Normandy crash lands on an alien planet. If the player's Effective Military Strength is high enough and Shepard chooses to destroy the Reapers, the game ends with a cutscene of Shepard taking a deep breath in a pile of rubble, hinting at survival. In a post-credits cutscene, an old man known as the "Stargazer" tells Shepard's story to a young boy, implying that Shepard's legacy lives on.