Right then, let us start from the beginning. The year was 2019 and Earth had gone on from it's lesser technolgy of yesteryear. Then there was the thing that started a whole chain of events that almost destoryed all of humanity. The wonder pill that had been made by Z and sons. The pill was advertised to cure any disease and lengthen the life span of any mortal who took it. Many people, of course, took the pill in hopes of curing whatever they had or making their somewhat meaningless lives longer than that intended by God. The pill worked amazingly enough, though the consquences were something that the sientists who had developed the pill or the people that had taken it had never foreseen.
The people who took the pill grew a hunger for the flesh and blood of humans and also, with any sort of scracth or bite, could cause an innocent bystander to become one of it's horrible breed... this was when the ears of humanity pricked up, this is when things started to go wrong. Armies were sent out in hopes of nullifinging the enimes, of which people refered to as 'zombies' but this only succeded in worsening the threat. In desperation the American president put out a secret to the masses about a place tha would keep them safe, the area 51's which had previously been massives caves underneath ground which the Americans had been building in, making large, fortified cites underground.
People rushed for the gates of the Area 51's, but, tragiclly, the idiot presidents of other countries did what humanity always did with something it didn't understand, fire nukes on it. Hah hah! Heh sorry, just my little joke. Anyway, the nukes blew up before many people got into the Area 51's, causing most of humanity to die in a matter of secounds. Some people did survive however, and these people, my friend, would become the last hope of not just our furture but of our planet.
Trapped
You have just woken up from being unconcious after having run into one of the Area 51 gates. The gate behind you have completely collasped, as have the others, except for one which has a gap big enough to crawl through. The undeground city lies ahead of you. Zombies have gotten into the Area 51's and will do anything to get their next meal, preferably you. You must survive in this dangerous world. Now is the time to fight against normality.