In the gripping drama Parts Per Billion, director Brian Horiuchi weaves together the interlocking stories of three couples facing an unimaginable crisis as a devastating biological disaster threatens all life on Earth. When a rogue nanovirus is accidentally released, the world is given a terrifying ultimatum: find a cure within forty-eight hours or face extinction. Amidst this apocalyptic countdown, Rosario Dawson and Josh Hartnett portray a couple grappling with the fragile nature of their relationship, while Penn Badgley and Teresa Palmer play newlyweds whose love is tested by the impending doom. Meanwhile, Alexis Bledel and Hill Harper struggle with the weight of past secrets, and Frank Langella and Gena Rowlands embody an elderly pair confronting the end with wisdom and regret. As the clock ticks down, each couple must confront their deepest fears, unresolved conflicts, and the true meaning of love in the face of annihilation. This emotionally charged film balances intimate human drama with the tension of a global catastrophe, creating a haunting meditation on connection, mortality, and the choices that define our final moments.