The Great Barrier Reef stretches along Australia's northeast coast as the largest coral structure on Earth, and NOVA cameras spend one extraordinary night there when the coral itself becomes the main event. Once a year, on a schedule tied to water temperature and the lunar cycle, the reef's coral colonies release eggs and sperm into the water within the same few hours, turning miles of ocean into a drifting cloud of pink and orange spawn. NOVA's crew films this mass spawning as it happens, alongside the fish, worms, and other reef creatures that time their own reproduction and feeding to take advantage of the event. The footage includes behavior and creatures captured on camera for the first time, shot in the water rather than reconstructed. Between the spawning sequences, the film surveys the reef's scale and the density of life packed into its coral structures, treating one night as a window into how the entire ecosystem runs on a single synchronized signal.