Fiona Sweeney wants to do something that matters, and she chooses to make her mark in the arid bush of northeastern Kenya. By helping to start a traveling library, she hopes to bring the words of Homer, Hemingway, and Dr. Seuss to far-flung tiny communities where people live daily with drought, hunger, and disease. Her intentions are honorable, and her rules are firm: due to the limited number of donated books, if any one of them is not returned,...