The strange story that makes up the unusual documentary The Missing Piece begins in 1976, when Trivial Pursuit champion Joe Medeiros turned up a shocking piece of information that had theretofore escaped his attention. He learned that in 1911, an Italian housepainter named Vincenzo Peruggia grew convinced that Leonardo da Vinci's Mona Lisa needed to be pilfered from the Louvre in Paris and returned to its "rightful owners," the Italians. Astonishingly, Peruggia then succeeded at lifting the painting from the museum, and held it in his Parisian one-room apartment for well over two years. He was never caught -- until he attempted to return the painting to Florence via an Italian art dealer -- which drew the attention of the authorities and led to Peruggia's apprehension. This documentary chronicles Medeiros' own 34-year quest to piece together the details surrounding the theft. As such, it includes an interview with the thief's 84-year-old daughter, Celestina Peruggia, whom Medeiros approaches in an effort to ascertain the reasons for Vincenzo's radical act.