In ancient times, Earth was involved in a massive conflict between Mental, an evil extraterrestrial being who wants to rule the universe, and the Sirians, a technologically advanced sentient alien race that left many of its artifacts to be discovered by humanity. In the 22nd century, Mental and his army of grotesquely twisted monsters return to Earth intending to destroy humanity. The humans are quickly overwhelmed and driven back to Earth. As a last resort, humanity uses the "Time-Lock". This mysterious Sirian artifact contains the power to transport a single person back to a chosen point in time. Because of his bravery in fighting these monsters, Sam "Serious" Stone is chosen to use the Time-Lock in hopes that he will defeat Mental and change the course of history.