On Enewetak Atoll in the Marshall Islands, a concrete dome sits over the crater left by a 1958 nuclear test, sealing in radioactive debris from decades of American atomic testing in the Pacific. The film follows the story of Runit Dome, built in 1979 as a temporary fix, and the islanders who were relocated so the US military could detonate dozens of bombs on their home. Interviews and archival footage trace the human cost of the testing program, from displaced families to lingering health problems, while the dome itself becomes the film's central image: aging concrete, cracks spreading across its surface, and rising seas lapping at its edges. Scientists and Marshallese residents describe what could happen if the structure fails and radioactive waste reaches the lagoon. The film treats the dome as both a literal container and a symbol of a promise made and only partly kept, asking who bears responsibility for a Cold War experiment still sitting exposed to the ocean.