In 1955, Peter Mangone was 14 years old - a skinny boy from the Bronx with a Marilyn Monroe fixation, like so many teenagers of his generation. What distinguished Mangone was that he got to meet his idol. For several months, he had played truant from school to stake out the Gladstone Hotel on Manhattan's East 52nd Street, where the 29-year-old Monroe was staying after her unhappy divorce from Joe DiMaggio and her dismissal from the Twentieth-Century Fox studios. One morning, Mangone borrowed an eight-millimeter Kodak camera from his brother, headed down to the Gladstone and met Monroe as she was on her way out shopping with her friend Milton Greene. Mangone's dream came true: she waved, winked and invited him along. Over the course of the afternoon, he filmed her intermittently, without sound, later developing the film and viewing it at home. When Mangone left home, the footage went missing, and was thought to be lost - until 2002, when his brother found it among their father's...