Max Harborn and his wife Eva, the first space explorers to visit Mars, discover an almost dead world of endless deserts. Lifeless, that is, except for a few curious Martian moths, paradoxically existing in the absence of vegetation and water. Two of the living moths are brought back to Earth, along with samples of rocks, sand, and atmosphere. But once back on Earth, the two moths, male and female, escape from captivity, and begin breeding at a prodigious rate. The alien grubs are capable of eating almost anything, and soon the world is imperilled by a horrifying destructive plague of the Martian moths...