An amateur sleuth suspects foul play when a fellow passenger on a seaplane suddenly dies. The third and final film with Edna May Oliver and James Gleason as the astute schoolteacher Hildegarde Withers and the New York Police Inspector Oscar Piper busy solving crimes.

The Office of Scientific Investigations tracks down the source of increased magnetism and radioactivity in Los Angeles, and discovers that a man-made isotope is consuming available energy from nearby mass every few hours, doubling its size in the process. Although microscopic, it will soon become big enough to destroy Earth; and how to stop it is yet to be determined. The film's Deltatron special effects footage is taken from the 1934 German sci-fi film GOLD.

Desperate to land a man on the moon before Russia does, NASA hastily preps a would-be spaceman for a mission that would leave him alone in a lunar shelter for a year.