04 - Juggernaut of Space by Ray Cummings

In a time of unimaginable peril, Earth stands on the brink of destruction, facing a doom beyond the wildest dreams of mankind. The world desperately needs its heroes, yet the only defenders available are five seemingly insignificant humans, trapped on a distant planet. Will they rise to the challenge and become the champions Earth so desperately needs? - Summary by Original Gutenberg text