As the story opens, Nancy and friends attempt to thwart suspicious, masked party-goers from reaching valuable objects d'art on display. At the party, Nancy finds an odd, black, velvet hood, which she retains as a clue. Her acquaintance, Linda, who is an employee of the Lightner company, is suspected of wrongdoing. At subsequent Lightner events, Nancy encounters other thieves, and is nearly suffocated by an evil pair of crooks. Nancy and George rent wigs to switch identities; however, George is kidnapped, her disguise removed, put under the influence of hypnotic, mind-altering drugs, and threatened.