Plot summary (original edition)

The boys investigate the mysterious disappearance of rare silkworms at a Scientific research facility while working at an Experimental farm during their summer vacation. The mystery deepens to include the theft of Government building materials- A case being investigated by their famous father, Fenton.

Plot summary (revised edition)

When two suspicious plane accidents occur near Marlin Crag Airport, the two Hardy brothers investigate the case and find themselves in greater danger than they anticipated.Frank and Joe suspect an oil beacon near the airport caught the pilots off track. The boys go to fictional Pittville and visit Martin Weiss's parents. They get a clue about a dance place called The Flickering Torch. This involves investigating the Flickering Torch where a band seems to be involved in something shady. Their friend Chet Morton develops a new hobby of building airplanes, however when he buys a used fuselage from an airplane junkyard it gets stolen from his farm. Ultimately the Hardys smash an illegal plot to make industrial diamonds using uranium isotopes from smuggled coal from the United Kingdom.

Original edition (1943)

• Ghostwriter: Leslie McFarlane
• Summary: While working at an experimental farm, the boys investigate the disappearance of valuable silkworms and the theft of government building materials.

Revised edition (1971)

• Revision type: Completely rewritten, with no plot elements retained from the original; the new story centres on a scheme involving smuggled uranium isotopes.
• Ghostwriter: Vincent Buranelli