In the Reynolds factory, a mysterious saboteur is secretly damaging airplanes, and Mugg's gang is at the center of the chaos. Mr. Reynolds enlists Danny's help to uncover the culprit, but their attempts only lead to suspicion falling on Dr. Nagel, a respected figure. Muggs concocts a plan to get closer to the doctor by having Danny fake an illness, but this inadvertently puts the boys in grave danger as the saboteurs mark them for elimination.
Flying Wild
A mysterious doctor is accused of using his air ambulance to smuggle top-secret documents to rival forces, shrouding his true intentions in secrecy.
