Forensic geologist Scott Wolter takes a one-man submarine into Rock Lake, Wisconsin, chasing a local legend that has circulated since the 1800s: sunken stone pyramids and a lake monster nicknamed "Rocky." The film follows suppressed 19th-century maps and surveyor accounts describing underwater structures, then surfaces at Aztalan, the fortified earthwork ruins nearby that some fringe historians link to a northern Aztec homeland. Wolter interviews divers, local researchers, and archaeologists as he weighs the lost-civilization theory against the more conventional explanation that the shapes on sonar are glacial debris and natural rock formations. Underwater footage from the submarine gives a direct look at what actually sits on the lake bottom, while historical documents and maps get pulled apart on camera for authenticity. The show does not pretend to settle the Aztec question outright, but it lays out the physical evidence, the folklore, and the competing readings of Aztalan's ruins clearly enough for viewers to judge the case themselves.