The planet is under attack by aliens, who might not be aliens but mutated humans, who are possibly mutated by real aliens actually from another planet, most likely hired by a big human corporation with very likely some connections with another species controlled by evil aliens from yet another planet.
And now: only a hero can save the planet..atleast that’s what everyone was hoping for, but since all heroes have now come and gone, you are the last option!
Go be the last hero!
Source: The Developer Website.