Don goes deep beneath the Great Lakes and explores flooded caves as he searches for evidence of a mysterious, cave-dwelling, pre-Clovis society that may have been the first people to reach America. Evidence presented: a mastodon image carved on a rock beneath Lake Michigan, 16,000-year-old poop and arrowheads from a dry cave in Central Oregon, and a 13,700-year-old human female skeleton from Cenote Naharon in Mexico's Yucatan. Nicknamed Eve of Naharon, she is the oldest human skeleton found in the Americas.

Don goes deep beneath Bagras Castle, a Knights Templar stronghold in Turkey, to explore a provocative theory that may link the fabled secret society to Freemasonry and America's founding fathers. He also explores the Old North Church in Boston, Massachusetts and Fort Mifflin in Pennsylvania.