Cannibalism has long been considered a dark chapter in man's history. Yet we think of it only as isolated occurrences. Now a Neolithic burial pit in Germany, found filled with expertly butchered human remains, challenges those assumptions. Archaeologists have never seen anything like it--the deeper they dig, the more bizarre the scene becomes. National Geographic joins an international team of experts as they reopen the earth to understand violent events as they played out seven thousand years ago.