I really liked the sound of this Ox character, I reckon the 3rd should be about developing his character a bit, and since he is a lot bigger (like described in the game) you can make that he is more able to fight off zombies than outrun them.
All the survivors in the mall have been killed and it starts with him trying to escape and find the guy that got away since he mentioned something about a farm in the countryside.
He is trying to make his way there and a whole lot of shit can hit the fan on the way, like what if the infection has started to mutate further? Since there could be a lack of humans Zombies are feeding off of each other, then they suffer from the virus twice as much, this could make them stronger faster, deadlier. He fights his way to the farm and arrives and it is in complete ruins.
Then the fourth could be back in the main character shoes describing what happened at the farm and why no one was there. Maybe one of the residents snuck out for a walk to get away from everyone or something, and came across a dog, the dog had been injured but animals are immune to the infection and they can only carry it. The resident hugs the dog the dog appreciates it licks his face, and the random now is a carrier due to saliva contact. He doesn't know this, he brings the dog back to the farm and its shot on site due to its wound, but everyone believes the resident is okay, then he gets sick and once again zombie shit hits the fan.
The options for a third and fourth are endless.
ultimatedown
possible set it in a time when the military is eradicating infected zones of all the living and infected indescrimetly.