The Shattered Helmet
by Franklin W. Dixon | 
The Arctic Patrol Mystery
by Franklin W. Dixon | 
The Haunted Fort
by Franklin W. Dixon | 
The Jungle Pyramid
by Franklin W. Dixon | 
The Mystery of the Desert Giant
by Franklin W. Dixon | 
The Masked Monkey
by Franklin W. Dixon | 
The Clue of the Hissing Serpent
by Franklin W. Dixon | 
The Sign of the Crooked Arrow
by Franklin W. Dixon | 
A Figure in Hiding
by Franklin W. Dixon | 
The Twisted Claw
by Franklin W. Dixon | 
The Clue of the Screeching Owl
by Franklin W. Dixon | 
The Witchmaster's Key
by Franklin W. Dixon | 
The Wailing Siren Mystery
by Franklin W. Dixon | 
The Bombay Boomerang
by Franklin W. Dixon | 
Danger on Vampire Trail
by Franklin W. Dixon |
The Mystery of the Chinese Junk
by Franklin W. Dixon | 
The Short-Wave Mystery
by Franklin W. Dixon | 
The Melted Coins
by Franklin W. Dixon | 
The Hidden Harbor Mystery
by Franklin W. Dixon | 
The Hooded Hawk Mystery
by Franklin W. Dixon |
Frank and Joe Hardy are determined to bring to justice the vicious criminals who kidnapped their detective father while he was investigation sabotage of a road-building project in the Kentucky wilderness. After Mr. Hardy's escape, the two young sleuths are spurred into action when he mumbles the word "Felix" and they discover a dossier of a notorious ex-convict was stolen from his files. The trail leads them to New York City but ends abruptly in a cemetery! With the new clue of a spiral symbol the boys head to Kentucky as part of a highway construction crew to track down the kidnappers and saboteurs.
