Brian Anderson and his wife Terri are attacked by mysterious creatures that emerge from the forest surrounding their Pennsylvania farm. They soon learn that several families on neighboring farms have also been molested by these alien beasts. Three human time travelers from a distant planet travel back to Earth to help fight the ravenous invaders they call Monstroids. Winnie, Sutra and Lacta are the descendants of the passengers and crew of Earth’s first commercial spaceship: a vessel that became lost and crashed on a habitable planet. These large, bald humans from the future must help the earthlings change history, for what is happening on Earth now will eventually produce a devastating impact on their home planet.
Brian and Terri quickly discover that the three well-endowed time travelers possess healthy sexual appetites. Two other couples, who have been driven from their homes, seek protection and shelter with Brian and his wife. The six earthlings and the three time travelers explore sex in a variety of ways and in creative combinations, driven by inexplicably potent lust.
The sex is fun, but survival becomes serious business when hordes of Monstroids appear. Winnie and the two males try their best to fend off the repeated attacks, but they find it hard to kill the alien beasts. The six earthlings take refuge in the cold, damp coal cellar in the basement of the Anderson farmhouse. Before the power grids fail and all radio broadcasts end, they hear that widespread panic and violence have become the norm across the state. Those from the future tell how their history recounts the total devastation of the planet Earth. This looks like the beginning of the end.
Sex is plentiful, but as food becomes scarce, the original optimism begins to fade among the “Cellar Six.” Those who must hide in the cellar face inevitable starvation if the Monstroids cannot be defeated. Shut off from sunlight and fresh air, the Cellar Six entertain themselves as best they can, but eventually moods darken and tempers flare.
Can history be changed? Will the Monstroids be destroyed? Can the human race on two planets be saved? Will the Cellar Six survive, and will the earthlings actually teach the three time travelers something new about making love?