Plot

The inhabitants of a small Illinois town begin disappearing after a strange cone is found sticking out of the ground nearby.

Strange things are happening in Riverdale, Illinois. A huge, seemingly alien structure has been found jutting out of the earth. Sent to investigate the origin of the mysterious object, Senator Walter Powers discovers that parasites from the center of the earth have infiltrated the town, taking control of the authorities and workers, making communication with the outside world impossible, and leaving the responsibility of stopping the invasion up to Powers and a small group of free individuals.—Jeremy Lunt <durlinlunt@acadia.net>

We open at night on the deserted streets of a small town. The narrator tells us, "A few weeks ago Riverdale, Illinois was just another quiet, small town. Then on that Saturday, shortly after midnight a living nightmare began." A man (an uncredited Hampton Fancher) carrying a lighted basketball sized glass container bumps into a pedestrian and the container is broken. A fight ensues and a hissing sound is heard. Title and credits follow.

A car, a 1956 Thunderbird, approaches. The narrator continues his story, "On Sunday, about an hour before nightfall, my fiancée and I were returning from a trip to her family's home in the country. Our wedding date was set. Everything was right with the world. We were on the way back to town to tell the good news to my father." The driver, Glenn Cameron (Alan Jay Factor as Alan Frost) and passenger, Elaine Cameron (Jody Fair) are distracted by the flash of a bright light. They stop to investigate in the nearby woods. They find three animals, "All of them, dead." They continue to walk and to their shock spot a large, cone shaped metal structure.

Two days later in Washington, D.C. a UFO committee reviews classified Army footage of the object. Senator Walter K. Powers (Cornelius Keefe as Jack Hill) and his assistant Dan Walker (Robert Ball) arrive late for the briefing. We learn that the object stands fifty feet high with a base diameter of fifty feet. The nature and origin of the cone is unknown. Dr. Paul Kettering (Ed Nelson as Edwin Nelson) is the chief investigator. Also noted is the coincidental slaying of several people in the nearby town. The Senator and his assistant fly to Riverdale to investigate first hand. They are met by Glenn who explains that his father, the Mayor, is missing. The three dive out to the site of the object. Alice Summers (Joanna Lee) is introduced. She is the Mayor's secretary, but she is assisting Dr. Kettering by recording test results on the object. The Senator climbs the scaffolding to question Kettering and his assistant, Dr. Wyler (David Hughes) on progress. Kettering explains that the object seems to be indestructible. He shoots a gun into the opening of the object and the bullet ricochets around and exits through the opening. Kettering crawls inside the object and explores. Sometime later, Dr. Wyler prepares to go inside as Kettering finally crawls out. A call to the site informs them that the Mayor has returned.

At his desk, Mayor Cameron (Orville Sherman) struggles as if possessed. He takes a gun from his desk drawer and fights to put the gun to his head. Kettering, the Senator, Alice and Glenn arrive at Town Hall. The Mayor acts very strangely. He is hostile and angry, even towards his own son. Kettering notices a strange, pulsating lump under the Mayor's jacket near his neck. The Mayor pulls a gun on the group. Kettering asks about the lump on his neck. The Mayor strikes his son trying to flee the room. As he does, Kettering strikes the Mayor who discharges several shots from the revolver. He is shot and killed by a deputy in the hall way just outside his office.

An autopsy on the body reveals something strange. The doctor (Doug Banks) and Kettering reveal the creature injected an acid into the Mayors nervous system. Even without the shooting death, he would have died within twenty-four to forty-eight hours.

The Sheriff (Greigh Phillips) drives back out to the object. On the way he encounters a man lying on the road. He gets out of his patrol car to investigate. He is attacked by the man. Another man, holding a lighted container, watches the fight. He sheriff is knocked out and the two men infect him with the contents of the container. The sheriff is revived and the three drive off in the patrol car.

Alice and Paul Kettering are working in the lab. He is experimenting with a piece of the creature taken from the Mayor. The parasite crawls toward Paul and attaches itself to his arm. He is able to free himself burning it with the Bunsen burner. Wyler calls Kettering at the lab. They drive out to the object. Glenn and Paul discover an electric utility truck which has been abandoned just off the road. Wyler has a theory. The object is an empty fuel section of a much larger object. A call to the Sheriff from the Senator goes unanswered. The sheriff struggles with his possession. Three groups are organized to search for other parts of the object. Paul and Alice find the body of the power company man. He has two puncture wounds on his neck. Glenn and Elaine are locked into a cabin on their search. Someone tries to burn the cabin down. Glenn shoots at the arsonist and he and his fiancée escape. The three groups reassemble at the Mayor's office. They discover two containers of parasites. The Senator calls the telegraph office to send a message to the Governor. The telegrapher (Henry Randolph) takes the message, but as he is also possessed, he sends the wrong message.

A car with three men drive up to Alice's apartment building. One climbs upstairs with a parasite and plants it in her room. She is possessed and joins the three men in their car. She is still wearing her nightgown. Paul and Glenn break into her room and discover she is missing. They drive back out to the object and discover the body of a dying man they recognize as Professor Helsingman (Saul Bronson). He, along with a scientific expedition team, vanished five years earlier. They discover the marks on his neck and take the professor to a hospital. Kettering questions the professor in his room. The only word uttered is Carboniferous, a geological Period about 200,000,000 years ago. Senator Powers tries to make several telephone calls, but is consistently told that the lines are busy. Glenn and Paul go to the telegraph office to question the man about the message to the Governor's Office. They are attacked, but manage to subdue their assailants and flee in the car. The Senator's radio broadcast is also sabotaged.

Kettering climbs up the scaffolding to check on his equipment. He discovers the two deputies on guard are possessed. They are both shot and killed. Kettering and Glenn enter the cone and discover a mist filled room. They are greeted by another member of the missing expedition, Professor Cole (Leonard Nimoy). The old, bearded figure tells Kettering he was Professor Cole. He explains, "Now I hold a position of a much higher order." He provides details of their invasion plan and adds, "We shall force upon man a life free from strife and turmoil. Ironic that man should obtain his long sought utopia as a gift, rather than as something earned." Kettering shoots and kills the lurking Sheriff. Cole disappears and the parasites chase the pair out of the cone.

Kettering formulates a plan utilizing the contents of the power company truck. He intends to connect a line from one end of the ravine to the other. He intends to use the cone as a ground. Another wire will be shot onto the wires of a very high voltage transmission line. Before Kettering can complete his plan, Alice appears on top of the scaffolding next to the cone. Paul walks back to the scaffolding to talk to Alice. He climbs the scaffolding to rescue the possessed Alice. She pulls a gun at shoots at Paul. Glenn fires the harpoon gun and the electrical connection is made. The cone is engulfed in sparks. Alice faints and the parasites inside are killed. The Senator and Glenn go inside to verify the menace is eliminated. Glenn and Elaine embrace. We close with a shot of the couple walking away as the camera slowly tilts up to feature the object and scaffolding.