Between roughly 17,000 and 7,000 years ago, melting ice caps raised sea levels by over a hundred meters, drowning entire coastlines where Ice Age people once lived. The film follows a team of divers and researchers investigating submerged structures off the coasts of India, Malta, and Japan, sites that sit far below where archaeologists expect human settlement to reach. Off Poompuhar in India, sonar surveys reveal what look like man-made walls on the seabed, and divers descend to examine stone formations at Yonaguni near Japan that some geologists read as natural rock and others read as worked terraces and steps. The film sets these underwater surveys against the flood myths recorded in cultures from India to the Mediterranean, asking whether they preserve a folk memory of the coastlines people actually lost. Marine geologists and archaeologists disagree on camera about what the sonar images actually show, and the film lets that disagreement stand rather than resolving it, leaving the submerged structures as evidence still open to argument.