Flying Wild (1941)

There's a saboteur at large in the Reynolds factory where Mugg's gang works building airplanes. Mr. Reynolds enlists Danny's help to try flushing out the saboteur. It doesn't work but it gets Muggs involved, who highly suspects the well-respected Dr. Nagel. Muggs has Danny feign an illness to get a closer look of the good doctor. That puts the saboteurs onto the boys, who then mark the lads for death.