As the name suggests this happens after a rather nasty event in the near future, aliens invade and attempt to wipe out humanity with a viral agent that they just call the Mutagen. As the aliens have experienced on countless other worlds, the mutagen warps the DNA of what ever species it comes into contact with, and changes them in random, violent, and always fatal ways….
Now the reason this is important is because, when they used it on Earth, everything happened to how they expected it to. But after a few months of deaths, and horror….. Humanity changed to accept the mutagen into their genetic structure. This allowed them to survive the plague, grow stronger, and become something else, they were Altered in such a way that the survivors were no longer base line humans. Humanity took to calling the survivors, Altered beings, and the Altered beings helped to win the war against the alien invaders, and send them back to the stars. Now adays you can find Altered beings in almost all aspects of Humanity.
In order for you to be able to install this game, you need to enable (allow) installation of applications from unknown sources (Unknown sources) in the phone settings. Usually this item is in the Security section