Don investigates an ancient cult by undergoing its most-terrifying ritual in Peru. He finds evidence of a supernatural war in remote caves and uncovers clues about bloody human sacrifices, revealing the truth behind a dangerous and secretive religion.

Don inspects ancient carvings in a British cave. He explores the alleged "witches' marks" ties to the supernatural as he visits holy wells, dives into a mysterious shipwreck and meets modern-day Druids to see if a bloody battle ended with a deadly curse.