#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.