Vault 11 was a well-stocked, sizable facility, with no drugs being pumped through the air or deadly plants that could infect everyone. Instead, it was part of a horrifying experiment that pitted the choices of mortality and morality against each other.
Upon arriving at the vault, the inhabitants were told that they must sacrifice one vault dweller to the computer each year, or everyone would be killed. The decision process was settled by a democratic voting system, and for many years people lived relatively comfortably, beyond the burden of the human sacrifices. The voting also led to the formation of several blocs, whose members would influence the elections heavily.
The most powerful bloc, named the Justice Bloc, one year threatened a resident named Katherine Stone into performing sexual favours for their members. In exchange, they wouldn’t vote for her husband, Nathan Stone, to be sacrificed. Although she complied, they voted for Nathan Stone anyway. In retaliation, Katherine Stone began murdering members of the Justice Bloc, confessed to her crimes, and got elected as both the Sacrifice and Overseer of the vault.
As her first act as Overseer, she replaced the voting system with a randomised lottery. The Blocs, unhappy with their power loss, staged an armed coup that resulted in only five survivors. The five survivors decided to commit suicide together, by defying the computer and refusing to sacrifice any one person. It was then that they made the horrifying discovery that this was exactly what the computer wanted, and they’d been living a sickening lie. It emerged that in the case of defiance, the computer would congratulate Vault 11′s populace on their selflessness and allow them to leave the vault if they wished.
Audio files discovered by the player indicates that upon this discovery, four of the five survivors decided to commit suicide anyway. The remaining Vault 11 survivor’s identity has never been revealed.