A few years ago, the world ended.
An incurable virus quickly spread, turning most of the human population into flesh-eating, murderous zombies.
When the angels realised what was going on and that there was nothing they could do to stop the overwhelming hoards, they left and abandoned humanity, or what was left of it, which isn't very much sadly.
You had been travelling with a group of survivors for the past few months and you had been resting in an old school. You all thought it was safe, and it had been until there was some sort of electrical issue which set off the school bell and lured the undead, causing you to flea. When you stopped to finally turn around, you realised that you were the only one who had made it and you were being chased by a couple zombies. You were unarmed.
Suddenly, you were surrounded by gunshots, your ears ringing painfully and the zombies were dropping dead, having taken bullets.
Exhaustion overtook you and everything went dark.
"I think they're human..." Sam said, slightly shocked to have found a survivor as he crouched down beside your unconscious body.
Dean still held his firearm and gestured to you. "Check for bites, anything. Gotta be careful, Sammy."
Sam respectfully checked you for zombie bites or any sign of infection. "Clean."
"Alright, let's get out of here." Dean looked around for a moment.
"Are we taking them... or..." Sam trailed off.
Dean looked at him as though he was stupid and sighed exasperatedly. "Yes. We're taking them, Sam."
Sam gently picked you up, hoisting you over his shoulder and the two of them navigated their way to their safe base of operation. It's an old bunker, quite a big place with many rooms. It was out of the way, in the woods, and pretty secure. What's more is that the place was stocked with supplies and weapons.
You were laid down on a couch in the library. Sam, the younger of the two brothers that had rescued you, was sat on a chair next to you, observing your condition and waiting for you to wake. Dean on the other hand was stood by the fireplace, watching the flames dance, lost in thought.