A fossilized skeleton nicknamed Ida sits at the center of this film, pulled from the Messel Shale Pit near Frankfurt, Germany, a disused quarry already famous for its fossils. Sir David Attenborough presents the case for what the bones might mean: the first complete skeleton ever found of an extinct primate called an adapid, a young female estimated at 37 to 47 million years old. She looks at first like a lemur, with the same tail and build as the ones still living in Madagascar's forests today, but the researchers who examined her argue she belongs to a different, related branch, one that eventually gave rise to monkeys, apes, and humans. That claim is contested, and the film lays out the reasoning behind it alongside the skepticism it has drawn from other scientists. The study behind the find was published in the Public Library of Science, and the documentary treats Ida's discovery as a test case for how a single fossil gets read as evidence in the story of our own ancestry.