High in the cloud forests of Peru is the mountaintop fortress of a lost civilization and an ancient legend of murder. The Chachapoya, or Cloud Warriors who lived over 400 years ago, vanished virtually overnight.

For years, anthropologists have been hunting for who or what killed these people. Now, the discovery of a site with more than 80 corpses could solve this mystery. National Geographic joins a team of archaeologists and anthropologists who believe the answer is hidden in the bones–testing theories from an Inca massacre or an epidemic brought by the Spaniards to a ritual sacrifice or assassination by a rival tribe to finally close the case on this lost capital's ultimate collapse.  (95 minutes)