When sent to investigate a Cerberus research base that's mysteriously gone silent, Shepard arrives to find geth overrunning the base. The sole survivor, Chief Scientist Archer, paints a dire picture: an experiment to fuse a human volunteer with a virtual intelligence created a dangerous hybrid "VI overlord". The rampaging VI has already attacked three other Cerberus bases, controlling any technology it finds in an attempt to break free--and unleashing geth across the planet. Unless Shepard can infiltrate the VI's fortress and shut it down, this homicidal intelligence will beam itself-off planet and wreak havoc on other systems.