Gravelle, a former baritone believed dead after an opera house fire, has been languishing in a mental institution for the past seven years, an anonymous amnesiac. When he fortuitously sees a news story about his former wife's current appearance at the local opera, his memory returns. He escapes, and, disguised in costume, seeks revenge for a failed attempt on his life years earlier. When the guilty parties are found stabbed to death, Charlie Chan and son Lee try to find out if the dangerous fugitive is the one responsible.