Divers Howard and Michele Hall travel to Fiji and the islands of French Polynesia to document one of the ocean's most fragile ecosystems before it disappears. Shot for IMAX by director Greg MacGillivray, the film follows the couple as they dive reefs threatened by warming water and coral bleaching, filming sharks, giant clams, and the dense reef structures built up over centuries. Interviews with marine scientists lay out why reefs matter beyond their color, as nurseries for a huge share of ocean life and as a warning system for how oceans respond to heat. The Halls' own history with these waters, decades of diving the same sites, gives the footage a before-and-after weight as they compare what they find now to what they remember. Large-format underwater cinematography is the point here, wide shots of coral cities and fish schools that television cameras of the era could not capture. It plays as both a nature film and a quiet argument for paying attention to reefs while they are still there to see.