Clue of the Black Keys

Its professor season, and Nancy is hot for teacher! Hardly the fuddy duddy Ned Nickerson describes, Professor Terrence is showing up at the airport and sweeping Nancy into the first mystery she's ever refused to take! When three couples kidnap one professor and his three obsidian keys, who will stop them from finding the treasure of the Florida keys, and unleashing a terrible secret? Nancy Drew and no less than four history professors, that's who!