#2 The House on the Cliff: When Mr. Hardy disappears while investigating a mystery surrounding a vacant house rumored to be either haunted or a hideout for criminals, the Hardy Boys search for the truth.
#37 The Ghost at Skeleton Rock: The Hardy Boys travel to Puerto Rico to investigate the mystery behind a secret coded letter that they received from their father.
#58 The Sting of the Scorpion: Frank and Joe witness an explosion in the sky near an airborne dirigible owned by Quinn Air Fleet. Facing danger from all sides, the boys decide to investigate the mysterious explosion.