Zombie Outbreak

A few residents began hungering for the flesh of the living, and gradually transformed into aggressive, insane humanoids. Bite by bite, each area suffered from the same fate as swarms of zombies shuffled across the bridges. You have armed yourselves with some pistols, and hope to restore this place to what it formerly was.

I'd advise securing a bridge with barricades, and then cleaning out the rest of the zombies in it with the shotgun pistol-using survivors. In total, there are 4 "islands" connected by bridges, so pick a small one and start killing those undead.