At five years old, Karen's dirt-poor mother succumbed to pneumonia, leaving her daughter behind. For four hellish years, she lived in an orphanage, where the other children picked on her mercilessly. Karen's only friend was her doll, Molly, the only gift her mother had ever given her.
One day, Harry and Helen Cooper came to the orphanage in search of a daughter, choosing Karen. The child was elated at the prospect of a new family that loved her, but would quickly learn what her true role was in the adoption. Harry Cooper ran a failing dry cleaning business, and needed someone that he didn't need to pay for their long hours of work. The man would verbally berate the child, and was never satisfied with her work. Helen Cooper said nothing, fearing the wrath of her husband if she intervened.
Harry's business inevitably went under. Later, he took his family along on an Harry's Cowardice
interview at a clothing factory several miles away. Stopping at a gas station, Harry discovers a zombie eating the attendant, and urged Helen back to their car. Unfortunately, Karen had wandered off, and Harry told Helen that she was just a girl, and that he wasn't dying for her. A ghoul bit Karen on the arm, but Helen managed to pull her to the car.
Harry drove the car into a ditch, forcing the family to flee on foot, as a horde of zombies overturned their car. The Coopers found a farmhouse nearby, and barricaded themselves in the basement. Karen was badly injured from the bite mark, unaware that she had been infected with the alien virus that would eventually kill her, and transform her into one of the creatures. Other survivors made their way to the farmhouse, but in the basement, Karen was unable to determine what was happening. The group discovered that the dead were being reanimated by a peculiar radioactivity from Venus that had blanketed the earth after NASA destroyed the Explorer satellite to protect the planet from the probe.
One by one, the group is killed off by the living dead, until Karen herself succumbs to the infection. When Harry stumbles into the basement after being shot by the truck driver, Ben, Karen has already turned. She leaps on her adoptive father, devouring his arm. When Helen finds her way to the basement, the undead Karen stabs the woman to death with a cement trowel, and finds her way up the stairwell to the living room. After attempting to attack Ben, the man barricades himself in the basement, and Karen wanders away with a horde of ghouls, prior to the arrival of a search and rescue team.