TOS Season 2 Episode 16 The Gamesters of Triskelion

Plot

The Federation starship Enterprise inspects an unmanned station at Gamma II. Captain Kirk, Communications Officer Lieutenant Uhura and navigator Ensign Chekov attempt to transport, but disappear before the system activates. Commander Spock orders a search for them and discovers an ion trail.
Kirk, Uhura, and Chekov find themselves in a gladiator arena on a strange planet. They are attacked by four humanoids and subdued. Galt, Master Thrall of Triskelion, informs them that they will be trained in games to entertain his masters, the Providers. Each is fitted with a "collar of obedience" that engages when they disobey Galt's orders. Uhura, Chekov, and Kirk are assigned individual "drill thralls": Lars, Tamoon, and Shahna, respectively. After a period of training, the Providers bid for the new thralls in their currency, "quatloos".
While running among ancient ruins outside the arena, Kirk tries gaining information about the Providers from Shahna, but her collar is activated when she speaks too freely. Kirk protests that he should have been the one punished, and when they are returned to their cells, Shahna expresses her appreciation for this. When she moves to embrace him, Kirk knocks her unconscious, and uses her key to free himself, Uhura, and Chekov, but they are stopped by Galt.
The Enterprise follows the ion trail, finding a planet with a humanoid settlement. As Spock and Chief Medical Officer Dr. McCoy prepare to beam down, the voice of Provider One warns them not to transport. Kirk's voice is also heard, and he brings them up to date. Kirk challenges the Providers to show themselves and finds himself in an underground chamber; The Providers are three disembodied brains. Kirk offers them a wager: he and his two officers will fight an equal number of thralls. If Kirk and his party win, the Providers will teach the thralls to govern themselves. If they lose, the Enterprise crew will become thralls. The Providers agree, stipulating that Kirk must battle three thralls alone.
As the Enterprise crew watches from the ship, Kirk kills two thralls and injures a third. Galt sends in Shahna. Kirk subdues her, and she surrenders. The Providers declare that Kirk has won the wager and unlock the thralls' collars. Shahna expresses a desire to follow Kirk to the stars, but he answers that she and the other thralls must first learn to live in their newfound freedom.