Serious Sam casts you as Sam "Serious" Stone a legend in his time, due to his extreme bravery in battle. As attempts to defend the solar system fail the planet Earth is coming under direct attack, and humankind stares into the face of its own annihilation. World leaders turn to their only hope, an ancient artifact called the "Time-Lock" that can teleport a single person back in time. The choice of whom to send is obvious: you are the only hope for humankind. Return the past and change it by exterminating the evil forces determined to end humanity.