In the near future, the planet Ebon launches an attack on Unified Earth. A crew of soldiers departs to the planet Ebon to take the war to their attackers, well aware that all troops before them have been lost, killed, or captured. Colonel Luke Stone is addressing his five-man team, but is interrupted when a high-pitched shrieking noise fills the ship. It shakes and Stone tries to tell them what to do if they are captured, but is cut off as the power goes out.
The six men find themselves on the planet Ebon. A voice from all around, the Ebonite Interrogator, demands that they identify themselves. Each one does: Stone of the U.S., Lt. Esra Krug of Germany, Major Jong of Asia, Lt. Terence Brookman of the U.K., Lt. Willowmore of the Free African Nations, and Private Arthur Dix of the U.S. The Ebonite Interrogator informs them that they are prisoners of war and are expected to cooperate in all ways. Their ship is destroyed along with those of their predecessors. The Interrogator orders them to proceed to the compound and Stone leads his men forward. As they travel through a vast chamber, Dix panics and finally tries to run. He collapses to the ground and one of the Ebonites, a black-skinned batlike alien, steps forward. The Interrogator points a wand-like device at Dix’s mouth and paralyzes his vocal chords.
Stone and the others take Dix to the compound and confirm that he’s okay other than being struck mute. A speaker box descends from the sky and the Interrogator speaks through it, saying they will soon meet in person and much more intimately. Stone steps forward as spokesman and demands appropriate food and bedding. The Interrogator tells him that they know about their needs from the other captives, and informs the soldiers that once they cooperate, their needs will be met. Stone asks for medical attention for Dix, but the Interrogator ignores him and says that each one will be accepted for an exploratory interview. He tells Dix that he is to be the first, ignoring Stone’s request to be chosen. A guard steps forward and Dix panics. As Stone and Willowmore try to calm Dix down, the guard uses his wand to blind Willowmore
Dix is taken to a cell and locked in. The Interrogator speaks over the loudspeaker and tells him to sit. Once he does, the Interrogator appears on a screen and has a guard bring Dix water. Once he drinks it, the guard leaves and the Interrogator tells Dix to speak truthfully. Dix only mouths his name, rank, and serial number, and the Interrogator tells him that won’t do. A vision of Dix’s mother applies, begging for her son to be spared. The projection disappears when Dix runs to it, and a man pounds on the door outside and demands to see the prisoner. The Interrogator invites the man, psychiatrist Dr. Whorf, to come in. He confirms that Dix isn’t suffering and explains that the Ebonites can control the senses. The doctor explains that he tested Dix during basic training, and he remembers the private as suffering from a self-destructive complex. Whorf tells Dix that he wants to die, and he’ll let himself be tortured and killed rather than say anything. The doctor tells Dix to fight his impulse and he’ll live, and encourages him to cooperate. The Interrogator dismisses Whorf, who leaves. Once he’s gone, Dix still refuses to speak. The Interrogator brings back the mental projection of Dix’s mother, and she encourages him to talk. He speaks and goes into her arms, and she tells him to whisper everything that the Interrogator wants to know. After a moment, the vision fades and the Interrogator tells Dix that he can go.
Dix returns to the compound and tells them that he can talk. When he mentions his mother, they realize that he was given a hallucinatory drug. Dix insists that he didn’t say anything to the Ebonites. The Interrogator orders Krug to come to his quarters. Willowmore breaks down, begging to go next so they’ll restore his sight. Muttering, Krug talks about how during World War II, his nurse threatened to tell the Nazis that he wasn’t a pure Aryan. He eventually turned in his grandfather. Krug wipes his face and then goes with the guard, and is confronted by a hallucination of his nurse. She says that Krug’s displays of weakness have convinced her that he’s not an Aryan. The projection fades and Krug screams in anguish, and comes to the next compound. Whorf is there, and tells him that he turned in his grandfather. A projection of his grandfather appears, forgiving him, and a sobbing Krug drops to his knees.
Dix insists that if any of them breaks, it won’t be him. Jong warns him that no one can resist torture, and is intrigued by the idea of Ebonite forms of death.
A glowing device is strapped to Kurg’s chest as he lies passively on the ground.
Stone wakes up in a cell as the Interrogator tells him he can go. As the colonel leaves, he glances back at the Interrogator on the screen and briefly sees two Earth officers behind him. When Stone looks again, the men are gone. The Interrogator reminds him to tell his men of Krug’s fate. As Stone leaves, the two men officers appear behind the Interrogator again.
Back at the compound, Stone tells the remaining four men that Krug went mad from the torture, and the Ebonites don’t permit madness on their planet. When they ask what he underwent, Stone says that it was routine interrogation and he dozed off. Willowmore asks for water, and Stone guides him to the common trough. Dix objects, saying he doesn’t want Willowmore’s hands in the water. There’s the sound of spaceship fire overhead, and the Interrogator tells Willowmore that a guard will lead him in for interrogation. Willowmore thanks them and goes, confident that his sight will be restored. Stone warns him not to let them seduce him with promises, and Willowmore says that they won’t.
Once the lieutenant is gone, Brookman notes that Stone dozing off in the middle of interrogation is a bit much. He dismisses him as a professional soldier, and Stone says that he refused to marry a woman who referred to him the same way. They both realize that they’ll become increasingly stressed as the hours go by, and Jong laughs. He explains that he was laughing because he felt confidence as they displayed human emotions. As long as they remain human, they’ll survive.
Willowmore returns only a few minutes later, and he tells them that the Ebonites offered his sight back because his blindness spoiled their “fun.” All he had to do was look at Krug’s corpse. Sobbing, Willowmore admits that he agreed. Jong tries to reassure him, saying that Krug would have wanted someone to see him. However, Willowmore says that the Ebonites took out Krug’s heart.
Brookman is next, and General Benton, the commander on the previous flight, comes in. The lieutenant is skeptical, but Benton says that it’s pointless to fight against brainwork. Brookman asks if he tried to fight, and Benton says that he was trained to save the lives of his men, and told the Ebonites what they wanted to know to save them. Benton, an old friend of the family, says that he owes it to Brookman’s parents, but Brookman says that his father’s heart is already broken and his mother’s is unbreakable. The Interrogator orders Benton out, and the general tells the alien that Brookman will be cooperative. Once he’s alone, Brookman recites his name, rank, and serial number. The Interrogator says that his patience is growing short, and he needs the code keys to anticipate the attack of the next ship. Brookman remains obdurate and the Interrogator summons a guard to take Brookman and prepare a chamber.
The two Earth officers examine files of the six crewmen. The commanding general chooses Dix, while the chief of staff chooses Stone.
Brookman returns to the compound and tells the others that the Interrogator meant for Jong to be taken to the chamber.
A guard interrogates Jong using the wand device, and the major tries to resist by reciting poetry.
As the others wait, the Interrogator provides nourishment bars and tells them that there no longer a reason to deny them basic necessities. He informs them that they will be treated with the honor and respect due a conquered enemy. The guard leaves, and Brookman suspects that Jong talked. Stone isn’t convinced at the neat solution, and Willowmore thought that Jong would die first. Brookman and Dix challenge him, and Willowmore insists that he didn’t give up information in return for his sight. Jong enters the compound and the others eye him suspiciously. Dix finally says that they have the privileges because of him. When Jong picks up a piece of food, Dix calls him a traitor and spits on him. Jong explains that he was strung up and tortured, but was never interrogated. He suggest that Krug talked, if for no other reason than that the dead make convenient scapegoats. Jong then shows them that the Ebonites crushed every bone in his right arm.
The Interrogator enters the compound and congratulates them on their decision to cooperate. He asks if they drew straws, and says that one of the previous crews used that method to determine who the traitor was. Stone insists that none of them is the traitor, but the Interrogator recites precise details of the next ship’s arrival. He assures them that they are ready for it and leaves.
Once he’s gone, Brookman insists that Jong is guilty, and spoke rather than lose his left arm as well. Jong claims that he blacked out before he had the chance to say anything, and woke up just as they returned him to the compound. The major then turns to Dix and suggests that he gave up the information in return for his sight. Continuing, Jong says that Willowmore would have bargained for his sight, or Stone might have been hypnotized. Finally he turns to Brookman and says that he’s impulse. When Brookman points out that if he had talked, they wouldn’t have interrogated Jong, Jong says they would have questioned him to confirm Brookman’s info, and recites the flight path. Stone says that he was the only one who knew the flight path, but Jong just said it. When Jong says that he heard the Interrogator recite it, Stone says that the alien broke off before he revealed that piece of data.
Stone takes out a handkerchief and rips it into four pieces. When Dix asks why, Stone explains that the chosen one will kill Jong. When Willowmore asks what the point is, Stone says that a traitor must be punished with death. He insists that they need all of the laws, even the painful ones, to remind them that they are civilized. Stone orders them to draw, but they hesitate when a spaceship enters the atmosphere above them. It’s shot down and Stone offers the pieces to each of the others. Brookman draws the short piece.
Jong casually eats a piece of food and waits for Brookman, who realizes that he’ll have to use his bare hands to kill the major. He advances on Jong but hesitates until Dix tells him to get on with it. Jong thanks Brookman for waiting until he’s done. Brookman finally breaks and insists that they can’t let the Ebonites make them less than human. Jong, amused, notes that human beings kill, but Brookman insists that he’s not an executioner and there hasn’t been a trial. When Dix objects, Jong asks him what he whispered to his mother. Dix insists that he said nothing, but then backs away, unsure. He remembers his mother giving him a candy bar in return for the information. Sobbing, he collapses as the others stare at him as he embraces empty air. Stone goes to Dix, who begs him to talk to his “mother.”
Laughing hysterically, Dix tells Stone that he believes his mother over him. He runs out of the compound and confronts an Ebonite guard. When Stone finds him, Dix is laying on the ground, humming to himself.
In the control room, the Interrogator informs the chief of staff and the commanding general that Dix has had a complete mental breakdown, Jong won’t recover use of his arm for at least a year, and Krug will die. The chief of staff notes that it was natural causes, but the Interrogator says that the charade must end and he will tell them the truth. It brings in Stone, and the commanding general complains that the Interrogator has spoiled the game. Stone demands answers, and the general explains that the whole thing was a test. Krug’s death was accidental, and the Ebonites tried to revive him but failed. Stone wonders if this confrontation is another hallucination, and the general orders him to feign ignorance so they can continue to test the others.
The general speaks of the war, and the Interrogator speaks up, saying that their attack was an accident. They agreed to do anything to make up for their mistake, but can no longer condone such inhuman methods. The general asks the interrogator what he knows of humans, and explains that during the Korean War, there was no resistance and 38% of their prisoners died of psychological surrender. He insists that they must induce artificial conditions to learn how the men will respond when Earth finally is at war. The two officers want to see how Stone’s men resolve the situation with Jong. When Stone says they were going to kill him, the officers say that they will try and save him, but the Interrogator is skeptical. Once the experiment is done, the officers will explain what happened to the men and free them. Stone snaps, refusing to countenance the experiments on his men, and the officers lead him away while the Interrogator backs into the shadows.
The three remaining crewmen wonder what happened to Dix, and Willowmore believes that they will all eventually be killed. Jong suggests they pass the time by plotting revenge on their captors, and Brookman and Willowmore agree to kill the next one they can. The Interrogator enters the compound and starts to explain what is really happening.
Stone and the officers run to the compound, realizing what the Interrogator has planned. The chief of staff yells that he can’t spoil things. Stone tells his men to release the Interrogator. The chief of staff draws a gun and threatens to shoot Jong if he doesn’t release the Ebonite. Willowmore disarms him and Brookman picks up the gun and shoots the officer before Stone can stop him. Too late Stone warns that the officer was real, not a hallucination