It's the one where you play as a sheriff and have to kill 100 zombies in the gas station.
Save your special weapons for after 40 kills or so. Kill the backpackers with headshots and they drop their backpacks; that includes the explosive backpacks. Save those for more important specials like fully armored Z's or massive groups, same with the anti-tank rockets. SMG is shit, Sparkshot is great but takes a long time so don't rely on it in a pinch, and flamethrower takes time to kill, so spray from safety (you can also ignite yourself by spraying an enemy or bit of environment that is too close). The corner across from the front counter, where the back door is to your left and the front door is down the aisle and to your right, is the best place to set up, but don't be afraid to do a loop if needed.
Now, that aside, on to the reason I pulled up the comments for the chapter: I think the release is why the more lighthearted chapter that deviates so much, since it went from that to a break. But it could also just be that they felt like changing it up a bit? Who knows.