As the Selene heats up and the air becomes unbreathable, young Captain Pat Harris and his chief stewardess Sue Wilkins try to keep the passengers occupied and psychologically stable while waiting to be rescued.

He is ready to abandon an initially unsuccessful search, when he is contacted by Thomas Lawson, a brilliant but eccentric astronomer who, from his vantage point on a satellite high above the Moon, Lagrange II, believes he has detected the remains of a heat trail on the surface.

To preserve air, most passengers enter a chemically induced sleep, with only Pat Harris and physicist Duncan McKenzie staying awake.

When the first caisson is sunk, disaster strikes again: the liquid waste of the passengers had been expelled out of the ship, turning the dust around it into mud, which causes another, smaller, cave-in.

After restoring these latter two, a new plan is made to sink the caissons, but now the bottom one has a flexible fitting attached to it which can be mounted to the sloping roof of the Selene.

The resulting breach is barricaded by the passengers, but dust is still pouring in and there is a fear that the burning material will cause the liquid oxygen supply to explode.

Meanwhile, Robert Lawrence is working in the rescue shaft: he sets a small ring charge to make a hole in the roof.

Galaxy reviewer Floyd C. Gale rated A Fall of Moondust five stars out of five, praising it as "emotionally gripping [and] astute" and that "it measures up to the very highest standard of his previous efforts.