There are heroes who walk among us: the clam digger who rescues a man from a burning retirement home; the dancer who prevents a robber from shooting two policemen at a nightclub; the former Marine, blinded during the Korean War, who saves two women from drowning in a river. What they have in common--besides the willingness to risk their own lives to save that of a friend or a stranger--is an unwillingness to brag about their actions. In 1904,...