A one-kilometer asteroid striking Earth would release roughly twenty times the energy of every nuclear weapon on the planet combined, and this BBC film follows the people whose job is making sure it never happens. In Arizona, astronomers work through the night at a monitoring station that scans the sky for new near-Earth objects, tracking each one's orbit to calculate whether it will ever cross paths with Earth. Researchers testing deflection methods appear next, firing intense laser beams at target rocks to see whether focused heat could nudge a real asteroid off course decades before impact. At NASA, astronauts train for a proposed manned mission to an asteroid, practicing the maneuvers needed to rendezvous with and work on a body with almost no gravity. The film moves between these three fronts, detection, deflection, and exploration, treating them as parts of the same problem rather than separate stories. It closes on the open question underneath all the technology: whether we would actually have enough warning time to act.