High in the German mountains, in 1980, a German soldier and an American officer from the United States Army Graves registration service search a snow-covered valley, looking for the remains of World War II soldiers. The searchers insist that a retreating Nazi troop and an American chemical unit fought a battle that killed every combatant. However, a local border patrol guard claims no battle was fought there, and disparages “ignorant” villagers who talk about “zombies.” The grave registration team camps on the mountain and continues its search, unearthing a skeleton in the snow. At night, zombies come into the campsite. The team shoots, but the bullets have no effect. The next day, the bodies of the search team are discovered, and the patrol officer insists he warned them of terrorists in the area. Nick Monroe, a Central Intelligence Agency (CIA) operative, is assigned to investigate chemical warfare “Special Unit C,” reported missing in action on that remote mountain in 1945. Nick is tasked with finding “Gamma Six Nine Three,” a lethal gas that Special Unit C developed, and tested on Nazi soldiers. Nick is teamed with biochemist Dr. Clarence Proud, a young-looking doctor who assisted in developing the gas thirty-five years earlier. Dr. Proud reveals that the principal scientist discovered the Army’s plans for his invention, and subsequently destroyed his notes and killed himself. Dr. Proud states that the gas is lethal, but he has developed a deactivating foam. Nick convenes with Dr. Proud at a restaurant in Germany, and is surprised to discover Proud’s niece, Susan, has clearance to join their team. A man, representing a German group interested in the investigation, follows Nick from the restaurant, and provides a list of missing German soldiers. Days later, Dr. Proud and Susan question where Nick has been. A waitress hands Nick a note with the name “T. Schefield” written on it. Nick rushes outside to meet with the man representing the German group, but two passersby stab the man to death. Nick chases the killers, and corners one in a basement. He shoots several times, but the bullets have no effect, and Nick knocks the killer unconscious. Nick goes to a camera shop that is a CIA front and asks to see the station boss. The clerk insists the station is closed, but Nick overpowers him and gets the address for the local CIA chief. As Nick leaves, the clerk is murdered by an unseen assailant, who eats him. Nick visits the address for T. Schefield, and a young soldier answers. He says his father, T. Schefield, has been dead for years, and claims to be a soldier who lives off-base. As Nick leaves, he asks the doorman how long the younger Schefield has lived there. The elderly man says three years. He corrects himself and states that he actually meant thirty years, but Nick has moved out of earshot. Nick meets with the local CIA chief, and questions why Nick’s informant was murdered. The chief denies his agents were involved, and Nick takes him to the basement to retrieve the unconscious killer, but the man is gone. They join Dr. Proud and Susan, and leave to search for the toxic gas on the mountain. As they set up camp, they are joined by the border patrol officer. Over dinner, Nick and the officer note their surprise at Dr. Proud’s youthful appearance. Proud serves a decadent dessert and declares he eats whatever he likes. Susan declines dessert and takes a walk. As a zombie attacks her, Susan screams and faints. Nick runs outside and shoots, but the zombie just laughs and walks away into the darkness. When Susan regains consciousness, she declares that a zombie attacked her, but Dr. Proud insists it was a bandit and demands more guards. Later, as everyone sleeps, a zombie sneaks into Susan’s tent and abducts her. Hearing her scream, Nick and the others search for her. The zombie drops Susan in the snow and is about to stab her, but the young Schefield stops him. Back at camp, Susan insists it was a zombie, and her uncle belittles her for being an hysterical woman. Although Nick believes it might have been a bandit, he consoles Susan and stays the night. In the morning, Dr. Proud is ill and remains in bed, but insists the others hunt for the gas. As Nick starts to search, the patrol officer suggests he take the deactivating foam, but Nick admits he is not looking for gas. In a remote field, he discovers skeletal remains. He spots a nearby building and sees Schefield in an Army uniform. When he returns to camp that evening, Nick tells Susan there are no zombies, but there are killers who do not want an investigation. That night, a guard is murdered by an unseen assailant, and his body parts are roasted over a fire for the killer’s dinner. The next morning, Dr. Proud is no longer ill. He joins the search in the woods, using a gas detection device. As he follows its signal, he runs into a young soldier, who declares he is from Special Unit C and wonders if the doctor remembers him. Dr. Proud runs back to camp, screaming hysterically. Nick calms him, and they discuss the existence of zombies. Nick decides to infiltrate the zombies, and dresses as an American Army zombie. On the mountain, a battle rages between the Nazi and American zombies. Some look healthy, while others are in various stages of decay. Nick joins them when they retreat to their headquarters after battle, and remains quietly in the background while Schefield notes the zombies will get their gamma rations the next day, and happily declares they have enough canisters to last two hundred years. The next morning at the campsite, Susan is at Dr. Proud’s bedside when he awakens. Proud notices his hands are decaying, and runs into the woods frantically searching for the gamma gas canisters. Nick awakens at zombie headquarters to find himself surround by skeletons, and feels sorry for them as he returns to camp. Susan is horrified when Dr. Proud, now a decayed zombie, returns and demands to know if Nick found the gas. Proud reveals he is seventy-seven years old, and should have died thirty-five years earlier. The gamma gas was originally developed to save lives by putting soldiers into a state of suspended animation until they could reach a hospital. Proud had an incurable disease and stole some gas to save himself. When the scientist who created the gas discovered the theft, Proud killed him, burned the laboratory to hide the murder, and accidentally destroyed the formula in the fire. Proud quickly discovered unfortunate side-effects from the gas. His flesh decayed, and to maintain a normal appearance, he had to supplement his diet with human flesh. Proud requires more gas, but the other zombies will not share it because they believe he intentionally destroyed the formula. Nick and the doctor fight, and Susan sprays her uncle with the deactivating foam. He turns into a skeleton and dissolves. Nick takes the foam and returns to zombie headquarters. The zombies received their dose of gamma gas, and are no longer skeletons. When Nick threatens them, Schefield admits they have observed him for weeks. He reveals they sleep during the day to save the gamma gas until they can develop more, and they eat human flesh to maintain a normal appearance. Not wanting to be ridiculed or subjected to experimentation, the soldiers plan to take revenge on the human race for turning them into zombies. While planning world domination, the soldiers alleviate boredom by enacting battles on the remote mountain. They ask Nick to join them and enjoy eternal life. He refuses and shoots bullets, but they laugh and insist nothing can stop them. Later, canisters of the gas sit outside Nick’s tent as he tells the visiting CIA chief about zombies and eternal life. The chief does not believe him, and asks about Susan. Nick states that she has gone out for a bite to eat. And the zombies continue their battles on the mountain.