We've Used It Once Before ...

Alien invaders conquered the entire human population, except for runaway scientists searching for a rumored artifact. Earth's leadership ignored an archeologist's wild theory about a prehistoric superweapon.

Dr. Sarah Watson, a believer, led her team deep underground. They discovered ancient ruins with an inscription, interpreted as:

"Here within lies the design for the superweapon. Use it once. Use it wisely. It wields the invader's technology—it shall trigger a celestial event to stop them but will also destroy all of your histories—a climatic cataclysm across the planet. Prepare yourselves for a new beginning. We've used it once before ..."