Two seas frame Saudi Arabia, and they could hardly be more different: the Red Sea, cut off and hypersaline, and the Arabian Gulf, a shallow basin formed only 10,000 years ago at the end of the last Ice Age, its waters warmed to the point of near-boiling in summer. David Attenborough narrates as cameras follow the animals that have adapted to each extreme, from coral reef life in the Red Sea to species that tolerate the Gulf's heat and salinity better than almost anywhere else on Earth. The film's centerpiece is a nighttime spawning event never filmed before: Palolo worms rising from the seabed in synchronized numbers to release their eggs, timed to lunar cycles. Produced by Icon Films with Saudi Aramco over more than a year, the production reaches waters that had barely been surveyed on camera before this project. The two seas sit only a few hundred miles apart, yet the marine life in each has evolved along separate paths.