Don examines the death case of Siamese Twins Cheng & Eng and unlocks their medical mystery. He studies an umbrella that played a role in a Cold War assassination. And, he visits a jail cell that holds a secret about Al Capone.

Don investigates the sinister secrets to a child's rag doll, studies a blueprint that holds the key to a deadly engineering disaster, and he examines a journal that inspired a fascinating work of American literature.