You were a lone survivor, just kind of wandering around the US during the apocalypse.

You got out of your truck and were constantly looking around to check for walkers, when one comes up behind you and tries to bite you.

There was a survivor in the distance, on the roof, a sniper (10K) watching it go down with the zombie in his sights.

A shot fires off, and the walker drops to the ground, dead. As you look around, you notice the sniper on the roof stand up and run off.