On December 26, 2004, an earthquake off the coast of Sumatra, the second-largest ever recorded, sent a wall of water across the Indian Ocean that killed roughly a quarter of a million people in a matter of hours. This film moves past the news footage most viewers already know to explain the mechanics of what happened: how a rupture along a fault line displaces enough seawater to generate a wave that can cross an entire ocean basin at jet-speed and still rise dozens of feet as it hits shallow coastlines. Scientists and engineers walk through the seismology of the quake itself, the physics of wave propagation, and the warning systems, or lack of them, that left coastal communities in Indonesia, Sri Lanka, Thailand, and beyond with no time to react. Archival footage of the wave hitting resorts and fishing villages is paired with expert interviews reconstructing the disaster hour by hour. The film's real interest is in prevention: what the world's oceans still lack in detection infrastructure, and what has changed since.