The Fifth Octave is a bit of science-fiction intrigue concerning little green worms from a different galaxy who want to take over the planet Earth because they like it here so much more than their home planet. These fat little worms are very intelligent and very inventive, and one of them, known as Lady V., has taught them how to hear in their minds what others are thinking and planning and how to go great distances and appear to be other people by using the fifth-octave vibrations that are too high for humans to hear. Humans hear them just as a kind of whispering. The worm leader, who goes by the name of Slobbo-his real name is too difficult to pronounce-is a kind of "wormsley" Napoleon, who wants and plans to take over much of the earth and make all the earthlings subservient to him. Many skirmishes occur where many earth people are killed, but very few worms. What was treated as a joke at first becomes a very serious threat. Finally, Slobbo is kidnapped and brought to a planet in the constellation of Orion, but he soon reappears on earth with all his fighting worms intact, making ready to take over. Slobbo has an earthling partner, named Marvin, who works with him because of jealousy on account of a botched love affair, and the two of them are put on trial. Slobbo is sentenced to be shot at sight. Lady V. convinces him to give up his heroic plans, which he does for a while, but then his need to be known as a heroic warrior overpowers him. Finally, the threat of disaster to his whole race of little green worms, including himself, persuades him to forget his heroic plans and become just a pleasant, normal worm.