In February 2001, a team of British, French, and Kenyan scientists announced a fossil find in Kenya's Tugen Hills that pushed the origins of the human line back further than almost anyone expected. The film follows the excavation that produced the specimen, nicknamed Millennium Man by the press, and the paleontologists who argue it may be the earliest known ancestor to walk on two legs. Researchers explain how bone fragments and dental evidence are used to build a case for bipedalism millions of years before Lucy, and the film sets that claim against the older fossil record and the scientific debate it triggered. Interviews with the scientists involved in the dig and the analysis lay out competing interpretations of what the bones actually prove. The result is a plain account of how a single discovery in East Africa reshaped, and complicated, the timeline of human evolution.