A boy accidentally fallen overboard… a child in a paddling pool… an old man taking a daily swim… These are their first prey. They arrive originally in ones and twos — deadly jellyfish eager to feast on human flesh. Attaching themselves lovingly to their victims' bodies. Then stinging… paralysing… feeding. Nothing can stop them — not even on dry land. Thousands surge over the beaches… fight their way inland up creeks and rivers… leaving behind their telltale smears of luminescent slime. But the final horror starts when they begin to breed. For now their young appear in reservoirs and storage tanks… slipping through drainpipes and water taps… And humankind faces ghoulish extinction