There is more to fear than The Dead
The winter is setting in. As ice and snow covers the land, Beth realises that it is a bad time to be on the road. If she doesn't find a place to settle soon then the cold will kill them as effectively as the zombies.
Carningsby presents them with a chance to see out the winter in peace. They leave behind the caravans and move into houses where they will be warm and safe. They have no idea that the town is already inhabited.
When The Townies make their presence known it is clear that The Convoy isn't welcome. When diplomacy fails, the two groups begin trading blows.
While they squabble over petty differences, a terrifying new sort of zombie heads towards them. If the two groups can't set aside their differences, they won't stand a chance of defending themselves.