"Summit Laboratory, come in, come in. Base to Summit. Are you reading?"
"Yes...yes....God, please, I'm...-"
"Summit Laboratory, this is Base Station. Come in!"
"I'm here - Oh please, please!"
"Base Station to Summit. Base Station to Summit. Come in!"
"You don't hear me, you don't hear me! - Oh God, oh my God - you can't hear me!"
Summit Base has lost contact with the lone research scientist 14,126 feet up on top of White Mountain, in California's Sierra Nevadas. The two scientists (Robert Culp and Eli Wallach, as Robert Jones and Frank Enari, respectively) whose research was the basis for the study - to test a number of conditions on monkeys, such as extreme cold and altitude, hypoxia, food deprivation, isolation, and fear, and extrapolate the findings for humans enrolled in the Space Program - are hustled into a helicopter, and flown to Tower Mountain Research Station, to find out what happened to the scientist, and to salvage the project, if possible. They bring with them a single chimpanzee, named Geronimo, as a control subject. The researcher, Vogel, is found frozen to death, seated in an unlocked room in front of a reel-to-reel recorder, snow drifting in through a partially open window. Some three hundred feet of tape has been recorded, but frozen, it's unplayable. The station itself is a wreck - food and supplies strewn about, papers and equipment scattered. The test subjects - six pig-tailed macaques and two chimps, are in their cages, lethargic, and nearly frozen. It's assumed that Vogel had gone mad, and sat in the room, exposed to the weather, until he died.
Horner, from Summit Base, wants the reel-to-reel tape sent back down, but Jones insists that it will shatter if moved. Besides, Jones and Enari agree, they transcribe all their work, so they need the recorder. Horner agrees, but only if the two will provide a transcript of Vogel's last words once it thaws.
The pilot, Val Adams, hastily acquaints Jones and Enari with the necessary duties of the station - keeping the generator and the heater running, shoveling snow from outside through an exterior chute, into a tank, so that a water supply, both hot and cold, can be maintained. He departs quickly, not wanting to be snowed in by inclement weather, taking Vogel's corpse with him. Jones and Enari are left alone with their chimp Geronimo, to clean up the station, and resume research on its test subjects. Geronimo is left uncaged, with free run of the station. They quickly divvy up their day-to-day duties. It becomes apparent that the two colleagues are miles apart in temperament. Jones, the theoretician, despises the minutia of research, and the confinement of the isolated station does not suit him. Enari, the practitioner, is delighted with this kind of work, and can't wait to get down to it. Although Jones is the one who puzzles the most over Vogel's inexplicable death - he discovers that the electonics room is the only one in the station that has an interior lockable door - it's actually Enari who's secretly the most disturbed by it, and reacts with anger when Jones can't seem to let it be.
Sometime during the first night, someone unseen rewinds and erases the reel-to-reel recorder.
Soon, other strange things begin to happen. One night, Jones is awakened by the screaming of the monkeys downstairs. He goes down to see what is disturbing them, but can find nothing amiss. Strangely, the door to the electronics room is ajar, and in it, the medical analyzer is turned on. Jones enters the room to turn it off, and becomes aware the the window is open. When he goes to shut it, the door begins to swing shut. He lunges for the door, catching it in time. Finding no explanation, he goes back upstairs to bed. "Frank," he calls to his colleague. "Are you awake?" Getting no response, he goes back to bed. But Frank Enari lies awake, his eyes suspicious.
The following morning brings panic. Both the generator and the heater have been turned off, and the water is freezing in the pipes. Swift action by Jones and Enari get them working again, but Enari thinks Jones is responsible. "Robert, I saw you - you went downstairs!" Jones tries to explain what he experienced, but it only seems to further anger Enari. The two begin to drift apart; Jones cannot stop trying to solve the death of Vogel, and Enari suspects that the strange occurences are being done by Jones. "It's not just the monkeys you're working - it's the monkeys and Enari," he accuses. Soon the two are barely on speaking terms.
One morning, after discovering the heat turned off, the running water gone, and the food supplies in the kitchen scattered and destroyed, Enari explodes. "You fraud, you fake! Robert Jones, the genius who's never arrived. You're not a man to be trusted; you never have been. Selfish, no morals... Why is it you haven't done great things in the world, Robert? What's the matter? It's certainly not because you lack ambition. You feed off other peoples' talent. That's why you have it in for me! I'm your meal ticket! Well, no more, Robert - no more!"
His tirade is interrupted by a crashing sound upstairs. Both of them run upstairs to the recreation room, to find Geronimo standing in the middle of the pool table, throwing the balls, and screeching. Enari starts to plead apologetically for accusing Jones, but Jones's anger grows like a storm. He seizes Geronimo, carries him downstairs to the monkey research lab, and padlocks him into a cage. Enari wants to make up, but Jones is too angry to discuss it. He prepares to go outside to shovel snow into the tank, so that Enari can have the shower he'd set out to have earlier.
After several unendurable sessions outside, Jones returns to the kitchen for a break. Enari is all conciliatory and contrite. He begs him to forgive him for what he said, and for letting Geronimo have the free run of the station. Jones remarks that Vogel's death can't be explained by Geronimo. Enari begins to say that he's willing to discuss that, but Jones cuts him off. Something else is bothering him, something they'd both heard that Vogel was supposed to have said in his final, irrational transmissions. Something about the monkeys' names. Jones returns outside to finish shoveling snow.
Enari has his shower. When he gets out, the monkeys are screeching and raising hell. He goes into the lab, and sees that Geronimo's cage is open and empty. He begins searching for him.
Outside, the light finally clicks on for Jones: the monkeys - Allie, Augie, Genji, Napy, Julie, etc., are all named for conquerors. He starts to trudge inside to tell Frank what he's figured out, but before he can reach the door, someone shoots the bolt from the inside, locking him out in the lethal weather. He beats on the door, calling Frank's name.
Frank, unaware of Jones's predicament, searches the other rooms, finally noticing a thin trickle of blood emerging from beneath a locked cupboard door. He opens it, and finds Geronimo inside, dead, beaten and torn. Geronimo drops out onto the floor.
Unable to get Frank's attention at the door, Jones trudges to the nearest window, beating on it. His strength is faltering; he is in danger of succumbing to the cold. He slowly makes his way back to the snow chute, to try to come in that way.
Enari bears the stiffened, contorted body of the dead chimp to the main room.
Nearly frozen, Jones crawls through the opening of the snow flap, over the tank. He loses his grip on the edge; slipping, his head and shoulders are immersed in the icy water. He struggles over the rim of the tank and falls to the floor. With great difficulty, he manages to stand up. Ice cakes his beard, eyebrows and hair to such an extent that he looks remarkably like the deceased Vogel. Breathing harshly, irregularly, he makes his way into the main room, where he finds Enari, the dead chimp lying on the kitchen table.
Enari is holding Adam's 22 pistol, pointing it at Jones. "I'm not gonna use this, Robert," he warns. "Unless... I'm gonna ask you simply, Robert. I want you to go into the electronics room. I'm gonna lock you in there and I'm gonna radio Horner!" Jones, breathing laboriously, stumbles to the table and collapses onto his knees. "I... couldn't have done this, you damned fool.."
"I - I'll go and bring down your bedding, Robert," Enari says, circling the table warily. "You're not feeling well." "I did not.. lock... myself... out, Frank." Enari helps Jones to his feet. "I want you to come along, Robert, please." "Who did?" Jones gasps. "You?" He looks doubtfully at Geronimo. "Him?" He grabs Enari's wrists. "For once in your life, face it - face it. We took food away from the monkeys, and food is taken... away... from us." Enari shakes his head in fear, disbelief. "It's no good, Robert - no good, no good -" "Subject the monkeys to fear, and we're subjected to fear..." "No!" Enari cries, pulling away. He points the gun at Jones, insisting, "You did it... you did it!" "Put them in isolation, and we become isolated!" "You've done all the damage you're going to do - ". Jones persists, "Subject the monkeys to cold, and we're subjected to cold." Enari grows panicked, backing away from Jones, who continues to shuffle forward. "I'm not gonna let you walk over me anymore, Robert, d'ya hear?" "Everything... that has happened... here... to us... happened... before -" "No!" "- to Vogel." "You're out of your mind, Robert - You're going out of your mind!" Jones slowly staggers towards Enari, pleading, "Look at you - you're becoming Vogel... being made to become like him!" "Oh, dear God, no -" "Vogel... told us the truth. He told us the truth, and nobody... listened! He told Horner, 'I had conversations with Alexander the Great!' What are their names? Julie... Napy... Allie!" Enari trembles, his eyes filling with tears. "Alexander the Great! Everything that we have done to them, they have managed to do to us! Frank, don't you get it?" he stumbles towards Enari. "No, please - " "It's the monkeys!" "NO!"
As he stumbles into Enari's arms, a single shot rings out. Jones slumps to the floor, dead. Enari kneels, touches the wound. There is blood on his fingers. In horror, he tosses the pistol away. Only the howling wind can be heard, but the silence is soon broken. It's Enari's own voice: "You don't like that, Robert, do you? Look at your face." Bewildered, Enari looks around. "Maybe now you understand how it feels," the voice continues, from another room. "Hypoesthesia, hypersensitivity." Then Jones's voice: "I don't know what you're talking about." Enari walks towards the source of the sound. "I'm gonna tell you what I'm talking about, Robert, and no bull. You're experimenting - with me." The voices emanate from the electronics room. Transfixed, Enari follows the sound into the room. "It's not the monkeys you're working, it's the monkeys and Enari. Every time I turn around, a light's left on, the window's open, the door ajar, the heat -" Enari finds it coming from the reel-to-reel recorder. "Look, I understand - no, I understand - maybe that - that's the way you go about doing things, right? - that's the way you like an experiment set up... But it's me you're experimenting with." Enari turns it off.
As he stands there, he suddenly becomes aware that the window is open, and the snow is blowing in. He goes to shut it. The window is frozen - it moves only with difficulty - and Enari hears the shrill creak of the door. It slams shut. As Enari stares, scarcely able to believe his eyes, he hears a key turn in the lock. Enari, like Vogel before him, is now trapped in the freezing room. And a small, furry face appears in the tiny, unbreakable window of the door - the face of Allie, who has again, like his namesake, conquered.