The images from Talos IV continue to transmit and Spock informs them they have no choice but to continue watching them: the Keeper has taken control of the screen. The images continue. Pike wakes up in an underground chamber and two Talosians study him. They are familiar with all of his reactions but say that he is more adaptable then most and they can proceed with their experiment.
On board the Enterprise, the crew deduce that the Talosians are master of mental illusions and plan to direct all ship's power through the lasers to blast open the entryway. Meanwhile, the Talosians begin their experiment and Pike finds himself on Rigel VII, where the crew were two weeks ago. Vina is there, dresses as a princess, and begs Pike to retreat with her into the fortress as an alien Kaylar attacks. Pike quickly realizes he's in another illusion but flees into the fortress. A Kaylar warrior attacks and searches the place for them. Vina begs him to attack but Pike refuses to perform for his captors. Vina inadvertently makes a noise and the Kaylar advances on them. Pike grabs a mace and defends himself, but the warrior knocks him off a ledge and grabs Vina. Pike grabs a sword and throws it into the Kaylar's back, injuring him. It leaps at Pike, who impales it on a spearhead. The illusion fades away and Pike and Vina are in their cell.
The Talosians stop the images for the moment and Spock explains that Pike is tiring and the Talosians wish to give him time to rest. Mendez demands an answer but Spock says that he'll have to wait until the end of the transmission, as the Commodore wouldn't believe him otherwise.
With an hour remaining until they arrive at Talos IV, the trial is reconvened and the images continue. Pike demands to know if Vina is real, and she suggests the Talosians may have made her out of his dreams. She says she can be anything he wishes to please him, and he tells her to prove it by asking her if there's a way to resist the Talosians' illusions.
On the planet's surface, Number One and the others are unable to burn through the elevator shaft leading to the underground city. Meanwhile, Vina offers to answer Pike's question in return for him selecting a dream for her to live in with him. She explains that they can trick and punish, and that thousands of years ago they lived on the surface. The surface was devastated by war and the survivors moved underground. They developed their mental powers but their illusions became a narcotic and they forgot to repair their machinery. Now they felt he emotions of their experimental subjects and live vicariously through them. They collected specimens long ago and Pike realizes they need a male and a female. Realizing she's said too much, Vina collapses in pain as the Talosian Magistrate/Keeper makes her suffer, and then cause her to appear to vanish.
The Keeper tells Pike to eat a vial of nutrients, and demonstrates an illusion of burning pain when he suggests he'll starve. He realizes they have limits and can't cause an illusion of pain. Angry, he drinks the nutrient and then throws himself at the transparent barrier. The Talosian retreats, startled, and Pike insists on discussing the fact that the Talosians can't read through pain. The Talosian ignores him and brings up Vina, and Pike realizes they want him to become attracted to her. He asks what they've done to her and the Keeper is satisfied with his protective attitude. They then place Pike in an illusion being back home at a picnic with Vina. He demands answers and Vina finally admits the Talosians can't read through primitive emotions, but it's impossible to keep emotional shields up forever. She explains that he's her perfect match so she can't help but fall in love with her. Pike admits he's attracted to her too, and she concludes he wants a fantasy, not something he's already experienced. Pike finds himself transposed to Orion where Vina is a green Orion slave girl. Pike begins to weaken and flees, only to find himself trapped in a tunnel. Vina is waiting for him.
Number One prepares to take a landing party down directly into the underground city. The transporter activates, but only Number One and Yeoman Colt dematerialize. They arrive in Pike's cell and find Vina clinging to Pike. She screams in anger, saying it's not fair and she did what the Talosians said. The Keeper informs Pike that since he was displeased with Vina, he now has two new specimens to choose from. Pike tries to block the Talosians with thoughts of hate and the Keeper punishes him with illusory pain. Pike refuses the others' help, trying to focus on his hatred.
Later, everyone rests in the cell and the Keeper enters a chamber next door. A panel in the war opens and Pike notices it. As the Keeper reaches for the newcomers' lasers, he pulls the Keeper in and threatens to break its neck. The Keeper assumes an illusion of a violent ape but Pike refuses to let go and the Keeper relents, but threatens to destroy the Enterprise through illusions. Pike doesn't believe the Talosians would indiscriminately destroy others. He uses a laser on the transparent barrier but nothing happens. Pike figure that it's an illusion and offers to demonstrate on the Keeper's head, and it drops the illusion to show the blasted portal. They leave for the surface.
In the present, the Enterprise arrives at Talos IV and Spock notes the natives control the ship. He directs their attention to the screen for the explanation. They watch as Pike and the others arrive on the planet's surface through the devastated barrier, which was earlier covered by an illusion. Number One is unable to contact the ship and the Keeper says they are now where they wished them to be, on the surface. The Talosians want them to start settling the surface, and Pike offers to stay and cooperate in return for Number One and Colt's freedom. Number activates her laser to self-destruct, refusing to let the Talosians create a race of slaves. Pike tells Vina and the Keeper to go, but Vina resolves to stay so the Talosians can't try again.
The other Talosians arrive and Number One stops the self-destruct. They give the Keeper the information they've assimilated, and the Keeper realizes that humans hate captivity and would rather die, no matter how pleasant it is. With no other species suitable, the Talosians are condemned to extinction. Pike suggests some kind of exchange but the Keeper warns that humans would learn the power of illusion and destroy itself in the same way. Pike sends Colt and Number One on ahead, but Vina refuses to leave with them. The Talosians drop their illusion of attractiveness on Vina, revealing a withered twisted form. The Talosians found her in the wreckage but were unable to restore her features. The Talosians assure Pike they'll give Vina back her illusion of normalcy and Pike, satisfied, leaves. The Enterprise crew has regained control and they leave.
In the present, Kirk turns to Commodore Mendez… who disappears. The Keeper appears on-screen and explains that Mendez was an illusion they projected. They engineered the court martial to distract Kirk from regaining control of the ship. The Talosians offer to let Pike stay there, living in an illusion and unfettered by his physical body. Spock admits he didn't want to explain to the captain what the situation was so they both wouldn't face the death penalty. Starfleet has seen the images and rescinds General Order 7 on this occasion. Pike agrees to go to the planet and Spock escorts him to the transporter room. On the screen, a physically restored Pike is reunited with Vina. The Keeper wishes him well with his reality.