is a science-fiction role-playing action game developed by BioWare for the Xbox 360 and PC. It is the sequel to Mass Effect and the second game in the planned Mass Effect trilogy. The story of Mass Effect 2 begins in 2183, not long after the events of Mass Effect take place. While on patrol to locate and destroy any remaining Geth, a race of sentient machines, the Normandy, and its commanding officer, Commander Shepard, comes under attack by an unknown assailant. The ship suffers extensive damage, forcing the crew to evacuate via escape pods. Joker, the helmsman, continues to pilot the ship despite the received damage to it and is rescued by Shepard, who drags Joker out of his seat and into an escape pod. Before he/she may board the escape pod, however, Shepard is sent flying and debris slicing through his/her suit as the Normandy is attacked once again. He/she suffocates and dies; his/her body is seen entering the atmosphere of a nearby planet. Commander Shepard's body is located and retrieved by Cerberus, an extremist pro-human organization, and, over the course of two years, attempts are taken to bring Shepard back to life through a project known as "Lazarus." Shepard awakens in the year 2185 aboard a Cerberus space station, which is under attack by hacked security mechs.

After he/she aids Cerberus agents Miranda Lawson and Jacob Taylor in escaping, Shepard is taken to a headquarters of Cerberus and granted an audience with the Illusive Man, who explains that Shepard was revived and 'upgraded' in return for his/her aid in combating a new threat in which human colonies have been attacked, their colonists deemed missing. Shepard and his/her team are dispatched to investigate the recently attacked colony of Freedom's Progress, located in the Terminus Systems. There, the group encounters Tali, one of Shepard's former squad members, and discovers that the mysterious insect-like Collectors were behind the attack and are responsible for the further abductions of other human colonies. Shepard reports this to the Illusive Man, who then places Shepard in command of the Normandy SR-2, a larger ship modeled after the original Normandy SR-1.




With the guidance of the Illusive Man, Shepard begins traveling across the galaxy to recruit a new team for what is assumed to be a suicide mission. The Illusive Man initially provides Shepard with four dossiers regarding potential recruits: a Salarian scientist, a mysterious vigilante called Archangel, a Krogan warlord, and a powerful but psychotic biotic. The Salarian, Mordin, is found on Omega and is working to stop a plague engineered by the Vorcha who are working for the Collectors. The vigilante Archangel is also on Omega, holding out on his own in a battle against three mercenary gangs. After reaching Archangel's hideout, Shepard learns that Archangel is actually Garrus Vakarian, one of Shepard's previous squad members. Garrus is seriously injured while battling the mercenaries, and, although he is permanently disfigured, he survives and joins the team. The Krogan warlord, Okeer, is found attempting to create the perfect Krogan through unethical genetic research; when the warlord is killed, he leaves his creation, Grunt, under the care of Shepard. The biotic, Jack, revealed to be a woman, is also known as "Subject Zero." Cerberus arranges for her to be purchased from the prison holding her; Shepard travels to the Purgatory prison ship. Once there, however, Shepard is betrayed by the warden as he attempts to capture Shepard for a bounty.

Shepard manages to escape the trap and rescue Jack, who joins the team despite an initial distrust of Cerberus operatives. After the recruitment of the four characters, the Illusive Man reveals that a human colony called Horizon has come under Collector attack, and he dispatches the team in an attempt to save the colony. He also notes that one of Shepard's surviving crew members, either Kaidan Alenko or Ashley Williams depending on choices made in the first game, is stationed at the colony to oversee the construction of massive defense towers. Shepard arrives with his/her team and battles the Collectors face-to-face; the group appears to have arrived too late as a majority of the colonists have already been taken away. Shepard later reunites with his/her former ally, who leaves feeling betrayed by Shepard working for Cerberus. After returning to the Normandy, Shepard is provided with dossiers on three more potential recruits: an Asari Justicar, a Drell assassin, and Tali. Shepard finds the Justicar, Samara, on Illium. She joins the team after Shepard investigates the Eclipse mercernary group and its involvement in a murder. The Drell assassin, Thane, is also found on Illium and is in the midst of an assassination mission. After learning of Thane's next target, Shepard fights his/her way to the top floor of the tower complex where the target is located.

He/she encounters Thane, who successfully dispatches his target and joins the team, as Shepard can provide him with a purpose. Tali is found on a Geth-occupied Quarian colony world, where she is researching the system's rapidly dying sun. After she is rescued from an immense Geth force, she agrees to join Shepard. The Illusive Man then reveals that the Omega-4 relay - beyond which lies the Collector base - requires a piece of Reaper technology in order for the Normandy to successfully navigate through it. It is revealed that Cerberus had located a derelict Reaper, evidently destroyed millions of years beforehand, and sent a science team there to recover the required device - an IFF transponder. During the course of the investigation, Shepard discovers that the Cerberus science team members have been killed. Battling his/her way through the Husks and Geth on board, Shepard recovers the IFF and salvages a damaged, but friendly Geth before destroying the core of the ship. Following the mission, Shepard may choose to either turn the Geth over to Cerberus for research or activate it. If activated, the Geth will identify itself as Legion and join the team against the Collectors. Shortly after, Shepard departs with the recruited members on a shuttle towards their next mission as the Normandy prepares the IFF for testing in his/her absence. A hidden signal is found, however, after the activation of the IFF, and Collectors ambush and board the Normandy.

Joker is forced to give control of the ship over to its onboard A.I., EDI - a potentially dangerous move. After successfully gaining control of the ship, EDI manages to pilot the Normandy away from the Collectors and rid the ship of all enemies, but the entire crew barring Joker is taken. After returning to the ship, Shepard's hand is forced - he/she can either continue completing secondary missions and sacrifice his/her captured crew, or he/she can go through the Omega-4 relay immediately to rescue the Normandy crew members. After traveling through the relay, the game may proceed in several ways due to several factors. Depending on whether or not Shepard enters the Omega-4 relay quickly, has upgraded parts of the Normandy, and has earned the the loyalty of team members, any combination of crew and team may survive or perish during the final mission, including Shepard him/herself. Regardless, Shepard fights his/her way to the core of the Collector space station. There, he/she discovers that the Collectors have been constructing a new human-like Reaper, made from the genetic material of the abducted humans and fused with the advanced technology of the Reapers. Shepard targets the weak structural points of the contraption, which is in the early stages of its construction, and it is seen collapsing into the lower confines of the area.

At this point, the Illusive Man contacts Shepard, suggesting that the team keep the station intact to allow research on its technology, under the pretense that any garnered information would be valuable in the coming war against the Reapers. Shepard may choose to either disregard Cerberus advice and destroy the station or use a radiation pulse to kill all the surviving Collectors and allow for Cerberus to take control of the station. After Shepard and his/her team destroy the Reaper, the surviving squad members escape to the Normandy and leave. A final cinematic shows the Normandy undergoing repairs following the mission; the Reapers awaken from their hibernation in dark space and descend upon the galaxy.

src : wikipedia, amazon.com