Star Trek: Bread and Circuses

On stardate 4040.7, the starship USS Enterprise, commanded by Captain James T. Kirk, is on routine patrol when it encounters the wreckage of the SS Beagle, a survey vessel lost six years earlier. The Beagle was under the command of Captain R.M. Merrik, whom Kirk knew during his academy days. First Officer Spock traces the path of debris back to the ship's point of origin, near the fourth planet in the previously unexplored FGC 892 System.
The Enterprise soon picks up an old-style television broadcast, with black and white video footage of what appears to be a Roman gladiatorial fight in an arena. One of the killed gladiators is named as William Harrison, who is identified by records as one of the Beagle's flight crew.
Kirk forms a landing party consisting of himself, Mr. Spock, and Dr. McCoy, and beams down to the planet to investigate. Soon they are captured by rifle-toting men, revealed to be escaped slaves, who bring the party before their leader Septimus. When the party introduces themselves as "men of peace", Septimus asks them if they are "children of the Son" – where the crew mistakenly hear "Son" as "sun" and think the inhabitants are solar worshipers. Kirk then responds by saying that they represent many beliefs. Septimus explains he was a former Senator until he heard the "words of the Son" and was made a slave. Although another slave Flavius, suggests killing the landing party, Septimus overrules him and decides the landing party poses no threat.
As Kirk pages through a gladiatorial magazine, he astounded to find the cultural development of 892 IV, called "Magna Roma" by the inhabitants, is so similar to that of the ancient Roman Empire back in Earth's history, but mixed with mid 20th Century technology. He refers to Hodgkin's Law, and the theory of Parallel Planet Development, where the two worlds developed the same but somehow the Roman Empire never fell, and took over the world. McCoy doesn't understand why they all worship the Sun however, since, as he states (incorrectly), Ancient Rome "had no Sun worshippers."
Kirk also finds uncanny similarities in one of the culture's leaders, Merricus the First Citizen of the Empire, to Captain Merrik of the Beagle and believes they are one and the same. Kirk explains to some of the slaves that he wants to meet this Merricus. Flavius then offers to help and leads Kirk to Rome; the capital city. The landing team puts on slaves uniforms, (grey tee-shirts with a chain symbol on the chest), and tries to sneak into the city. Along the way, Flavius explains how he was once the greatest gladiator until he too heard the words of the Son. The way of the Son involves a bond of brotherhood and a commitment to peace; it was hard for a fighter to accept, but "the words were true."
They are soon captured by Roman guards (who appear like a police state riot squad), and are placed into the slave pens. Kirk asks Flavius about the culture's institution of slavery. He discovers that a slave who performs well earns health benefits and if he survives long enough, is also compensated in the end with retirement benefits and prestige. McCoy and Spock get into another argument about logic and Flavius asks if the two are enemies. Kirk replies "I'm not sure they're sure." Kirk asks Flavius how long ago the slaves started worshipping the Sun and Flavius says as long ago as the founding of the empire.
Later, the landing party makes an escape attempt while the guards lead them to meet Merricus. Merricus, however, has anticipated their escape and has forces waiting to apprehend them. Once again, the party is taken prisoner and they stand before Merricus and the Proconsul Claudius Marcus who dismiss the guards and invite the landing team to sit and talk in private.
There, Merricus admits that he is Captain Merrik. He explains his ship was severely damaged in a meteor shower and he stopped at 892 IV for repairs. When he beamed down, he met Claudius Marcus who demanded that word of the planet's culture not be divulged to the Federation for risk of cultural contamination. Merrik decided to stay and put whatever crewmen who refused to remain behind into the gladiatorial pits where they would certainly be killed. Merrik then informs Kirk that word of the planet's society must not leak off the world, and that the Enterprise crew must also remain behind. He tells Kirk to order the crew to abandon the ship and integrate into Magna Roma's culture.
Although he is threatened at gunpoint by armed guards, Kirk refuses Merrik's demands and instead he tells Mr. Scott "condition green" on the communicator; this is a code-phrase indicating the sender is in trouble, but that the recipient must not attempt a rescue. Angered, Marcus sends Spock and McCoy into the arena for Kirk's defiance.
Spock and McCoy must face off against Flavius and another gladiator, Achilles, under a set of studio lights, television cameras, and an obviously fake backdrop of a Roman combat arena. The whole scene looks more like a violent game show. The battle begins as Spock quickly overpowers his opponent, and when McCoy is in trouble, Spock nerve pinches his assailant ending the fight to a hail of boos and hisses from a "pre-recorded" crowd. Spock and McCoy are taken back to the slave pens and Kirk is taken to stand execution which will be televised live.
Kirk goes to his room where a woman, Drusilla, is waiting for him and says she is his slave. Elsewhere, Spock and McCoy are placed in another cell. McCoy tries to thank Spock for saving him in the arena, but Spock shrugs him off. McCoy tells Spock he really does care, but is just afraid to show it. Kirk meanwhile, eats and talks with Drusilla and then goes to bed with her. Marcus later explains that he arranged it all because he respects Kirk as a real man, equal to the Romans, and wanted him to enjoy his last hours as a man.
In the meantime, Mr. Scott works on a way to disrupt power and communications on the planet while obeying the Prime Directive not to interfere with a planet's society. He blacks out the city just before Kirk's execution. In the diversion, Kirk frees Spock and McCoy but is soon captured again. Merrik however, does something unexpected, and radios the Enterprise to have Kirk and his party beamed back. Before he can complete the message, Marcus kills him for his treachery. Scotty understands the message and the landing party dematerializes just as they face a hail of machine gun fire.
Back on the ship, Kirk commends Scotty. Spock expresses curiosity to Kirk and McCoy as to why the slave "Sun" worshipers seemed to adhere to a philosophy of peace; again incorrectly, Spock says that in most societies sun-worship is a primitive religion of superstition, with no philosophy behind it. It is at this point that the landing party learn the true meaning of the repeated references to the "Sun/Son". Uhura, who's been monitoring radio transmissions from the planet, informs them that the worshipers are actually referring to a "Son," rather than "Sun," as in, "the Son of God." Kirk replies in realization: "Caesar ... and Christ; they had them both," referring to a historical figure of war, and a historical, messianic figure of peace, making obvious note of the continued parallels of this planet's history to Earth history. Kirk remarks that it would be interesting to observe this period of time on the planet below.