Man, this one reads like terrible fanfiction.

If anyone's seen the show Heroes, you know where Hiro met Charlie?  In that little coffee shop?  The dream starts off there.  I'm just hanging out or whatever, then everyone in there realizes that zombies are attacking.  Not sure what to do, I panic, because they're about to attack me.  Suddenly, someone busts down the door to save the day.  I look over and see the silhouettes of Zoey, Francis, and Bill from Left 4 Dead.  Then it occurs to me...I'm Louis.  And this is how we meet.  We don't even get to exchange names before someone yells "TANK!" which immediately preceeds the tank bursting through a wall (Kool-Aid man style).  We all make a run for it, shooting zombies that get in our way.  Outside the cafe is a big open field which ends at a cliff overlooking the ocean (remember that from Heroes?  Me neither).  We decide to make a jump for it.  The dream ends with me trying to outrun the tank so I can jump in the water. 

The dream got me thinking...how cool would prequal missions be as downloadable content for Left 4 Dead?  Each one could tell the story of how each character came to find themselves with their motley crew.  (And since you would need to start as just one or two characters from the real game, the other players could be NPCs that get killed when meeting the next character.)