So, 80% chance all the L4D fans in the PPC already know about this, and as usual I'm the last to find it, but...

Through TV Tropes, I found this: http://www.fanfiction.net/s/5984812/1/Two_Step It's called Two Step, and it takes place post-canon of Left 4 Dead 2. Basically, Nick, now a Handicapped Badass thanks to the loss of his eye, is separated from the others. The entire fic (29 chapters so far, and still in progress) is about him dragging himself through the metaphorical midden to get back to them. The fic has plenty of opportunities to plunge into OOC or Narm territory, but it never does. The characterization is great, and the plot is gripping enough to drive me to stay up until 2 in the morning to reach chapter 23 in one day.

Also, you might want to have a box of tissues within reach.