Each night for twenty nights you have to defend a barricade from hoards of zombies. During the day you can allocate twelve hours of time between repairing the barricade, searching for better weapons and searching for survivors who will help you repair the barricade by day and defend the barricade by night.
General Tips
Don't wast time keeping your barricade in perfect condition. There seems to be a magic six hour number to finding survivors and the chainsaw is an awesome secondary weapon.
The final weapon in the game is an awesome weapon that will allow only the very fastest zombies anywhere near the barricade, but to select it you have to first find it after getting all the other weapons in the game and then once you have it, select it by click on the maps at the bottom of the weapon's locker, as it is invisible. You can see the effects on this screenshot below.
