Earth colonists on Ganymede, the largest satellite of Jupiter, have discovered the existence of intelligent life on the planet's surface.

Although the force field can be created, it cannot exist for more than a fraction of a second at the strength needed to contain Earth's air pressure, let alone Jupiter's.

Nicholas Orloff, the Colonial Commissioner (who had been on Ganymede to assess the threat) reports back to Earth that the danger that had been posed by the Jovians is ended.

The story illustrates a tension between the theoretical ("Scientific") attitude and the practical ("Technical") one, exemplified by the prominent scientist claiming that his theory shows the force-field technology to be impossible ("That's final!

[1] After selling "Nightfall" in late April 1941, Asimov took a break from writing to study for qualifying examinations to enter the PhD program in chemistry at Columbia University.