1899, July 5th A mysterious virus has swept the American continent, dubbed "Zombie plague". You and 4 others people had to evacuate to Mexico because well... The Mexican scientists had created a cure for the virus. Upon reaching the Fort Constitution, you accidentally made a mistake by firing a cannon on the outpost. As the zombies with U.S Army uniform, wielding Cavalry Sword, Navy Revolver slowly walking out of the barracks, it was like they still have a bit of order to protect the US property even though they're zombies...