You are a citizen of Vault 53, located in upstate New York, or so you have been told. Your people have lived in this vault for almost two hundred and fifty years, waiting for the day when the vault's sensors tell the Overseer that the surface is safe to settle. Your entire life, you've been brought up on holotapes of the beauty of the surface, the worth of the American way of life. You've lived in what you're been assure is the greatest triumph of prewar technology, a vindication of everything America stood to protect from the godless commie hordes.
But you've also lived a life of constant malfunctions, one major piece of equipment failing after another. Even with a population of nearly a thousand, everyone from the Overseer down to the lowliest hairdresser has had to chip in in their own way with repairs. Nothing has broken permanently, but the repairs and maintenance has been a constant part of your life. Until now. At long last, after nearly two hundred and fifty years, something has broken that even the chief engineer can't fix. The Manufacturing Governor Chip has fried, and without it the Vault can't fabricate any new material. Only a small problem at first, but with time...
This failure, kept from the general population, has brought you here. After some discrete inquiries, the Overseer has asked all of you to meet him in his office. The subject of the meeting? Leaving the Vault. For the sake of saving everyone, you have been asked to be part of an expedition surface, to find the parts to replace the MGC. Or else a suitable place for the citizens of Vault 53 to settle. It's something that has been just a distant idea for your entire life, but now you find yourself faced with the prospect directly. Seeing the surface. Meeting new people.
Leaving the Vault.