Dr. Aris Thorne, a geophysicist, remains on Earth after humanity's evacuation due to a dying sun. She's dedicated to a risky experiment: reigniting the sun. Her research unexpectedly reveals a sophisticated subterranean civilization thriving within Earth's core. This discovery throws her plans into disarray, forcing her to reconsider humanity's future and the meaning of survival. The subterranean civilization, advanced in ways she couldn't have imagined, offers a different path to survival - a path that involves collaboration and potentially abandoning her initial plan to restore the sun. Aris wrestles with the ethical implications of her actions, facing the potential devastation of the subterranean civilization alongside the potential extinction of humanity in space.