In 1795, a teenager discovered a mysterious circular depression in the ground on Oak Island, in Nova Scotia, Canada, and ignited rumors of buried treasure. Early excavators uncovered a clay-lined shaft containing layers of soil interspersed with wooden platforms, but when they reached a depth of ninety feet, water poured into the shaft and made further digging impossible.

Since then the mystery of Oak Island's "Money Pit" has enthralled generations of treasure hunters, including a Boston insurance salesman whose obsession ruined him; young Franklin Delano Roosevelt; and film star Errol...