Frank and Joe Hardy are determined to bring to justice the vicious criminals who kidnapped their detective father while he was investigating sabotage of a road-building project in the Kentucky wilderness. After Mr. Hardy's amazing escape, the boys pick up a clue -- the word "Felix" mumbled by their sick father in his delirium. When they discover that the dossier of a notorious ex-convict has been stolen from Mr. Hardy's files, the two young sleuths are doubly spurred to action. The trail leads them to New York City but ends abruptly in a cemetery! Stunned, Frank and Joe come upon another clue -- a spiral symbol. Aided by their pals, the boys take jobs on the highway construction crew in Kentucky to try to track down the kidnappers and the nefarious saboteurs. But who among the crew is friend and who is foe? In a desperate maneuver that almost costs them their lives, the Hardys bring to a spine-tingling close one of the most action-packed and suspenseful mysteries they have ever solved. - Flyleaf.

The Hardy boys bring to justice the vicious criminals who kidnapped their father while invesigating the sabotage of a road building project.