Hold the Line
The zombies want to get to your outpost, so they can eat the people there. Tonight, you would be alone to kill them since all the others would be sleeping. It would be up to you to hold the line till its morning. In this game, you would need to make sure that no zombies can get close to your base. You would need to hold the line for now. You can make money from killing them and you can spend the money on the guns after each level. The game would be harder, so you would need better weapons.