In 1924 at age 56, Bertha Hummel Cox left her comfortable life in Wisconsin to become a missionary for indigenous tribes in the Amazon rainforest. She had no idea that it would take nearly four years of frustrating delays and treacherous travels to reach her destination. Among her many challenges were months of isolation in a make-shift hut in a remote forest and a death-defying experience on one of the world's most dangerous stretches of whitewater...