The Flickering Torch Mystery — Franklin W. Dixon

Two unexplainable plane crashes near an airport on the East Coast plunge Frank and Joe Hardy into a bizarre case. From the moment Frank and Joe find a radioactive engine in an airplane junkyard, unexpected dangers strike like lightning. Despite the repeated attempts on their lives, the teenage detectives pursue their investigation, discovering two vital clues and others that provide the solution to one of the most baffling mysteries the boys and Mr. Hardy have ever encountered.