After a year of marriage, Marge Farrell is despondent that her husband Bill is cold and not acting toward her the way he did before they were married. He does not show any signs of genuine affection towards her or toward his new dog, a surprise anniversary present from Marge. The dog barks and snarls at him whenever he approaches; he kills it in their basement, telling Marge the dog was strangled by his collar while pulling on his tethered leash. She is also becoming concerned because, wanting a family, she has not become pregnant. After undergoing various tests, her doctor assures her that she can have children; he suggests that Bill come in and see him to be tested. She soon notices that other husbands in their social circle are acting the same way. One night, she follows Bill when he goes out for a long walk. He heads to an isolated area in the woods, where she discovers that he is not the man she thought she married but an alien impostor. An extraterrestrial life form leaves Bill's body shell and then enters a hidden spaceship. Marge is horrified at the prospect and tries to warn others of the alien plot, but too many men in town have already been taken over, including the town's Chief of Police, who does nothing after hearing her story. She attempts to call
Washington, D.C., but all outgoing phone lines are busy. She attempts to leave by car and the local police stop her, saying that the only exit bridge which leads out of town is down. When she tells “Bill” that she knows he is an alien, “Bill” tells her their plan: all the females on his planet are extinct. He and the other males of his species are taking over human bodies so they can have offspring with Earth women. However, their scientists must modify the bodies for this purpose. They did not foresee that the memories of the host bodies would result in them experiencing love for the first time (their species, unaccustomed to forming emotional relationships, used their females only for breeding purposes). Marge finally convinces her doctor, and he gathers a posse of men who recently fathered children and therefore cannot be disguised aliens. They attack the aliens in their hidden spaceship. Bullets cannot hurt the invaders, who are surrounded by a force barrier. The aliens, however, prove to be defenseless against a pair of
German Shepherds being used by the posse. The aliens are killed when the dogs attack, all except the alien posing as Bill. One dog and a posse member are disintegrated by the alien's rayguns during the fight. Entering the spaceship, the posse finds that all the human male captives are unconscious but still alive, including Bill. Each man is hooked up to an apparatus that keeps them alive, while a duplicate “shell” is created for an alien to inhabit. The posse begins to disconnect the captives, which kills the aliens one-by-one. Shortly before his faux human body is destroyed, the alien occupying the Chief of Police broadcasts a warning to his people in orbit that they have been discovered by the humans. Thereafter, a fleet of alien spaceships is seen leaving orbit. They must seek out humanoid females elsewhere now that their breeding plan on Earth has been discovered. The humans that were disconnected from the ship are escorted out of the ship alive just before it explodes, reuniting Marge with the real Bill. ==Cast==