The Italian secret police have called Nancy Drew in to investigate a series of art thefts happening in Venice. The thief has been dressing up in a mask and cape, and the news media have begun to call him "The Phantom" not only because of the way he dresses, but because he leaves behind so few clues. A crime syndicate is actually responsible for the thefts, using commedia dell'artecharacters as code names. Nancy is sent to spy on the ring and discover the ringleader of the crimes.​