Treasure hunters Peter Lindberg and Dennis Åsberg are scanning the floor of the Baltic Sea when their sonar picks up something nobody expected: a roughly 200-foot circular, cylindrical formation sitting where nothing but seabed should be. The film follows their dives and the equipment they bring in to get a closer look, then widens out to the geologists, marine scientists, and skeptics who each take a turn at the sonar data and underwater footage. Theories stack up fast, a sunken warship, a natural rock formation shaped by glacial forces, a sonar glitch, and, for the more speculative voices on camera, the remains of something built rather than formed. Interviews with the divers sit alongside expert breakdowns of the imaging technology used to map the object's shape and composition. The film does not resolve the mystery so much as lay out how far serious analysis has gotten and where it still stalls, leaving the Baltic Sea anomaly exactly where it has sat for years: unexplained, photographed, and argued over.