The Enterprise visits a planet that had previously been visited by the U.S.S. Horizon 100 years earlier, before the issuance of the Prime Directive. The Enterprise received an old radio-style message before that starship was lost, which reported an intelligent, developing alien species prone to imitation. The Horizon left behind a book about gangs of 1920s Chicago which became the Iotians’ bible. They are divided into a series of criminal gangs, two of which are headed by Bela Oxmyx (Anthony Caruso) and Jojo Kracko (Vic Tayback). After beaming down, Kirk, Spock, and McCoy find themselves in the middle of a turf battle. Both sides take turns holding our heroes hostage and demanding “heaters” (guns) from the Federation in order to take control of the planet. Kirk must do his best to fix the wrongs of the Horizon w/o interfering too much with the development of the planet’s evolution.
This ep has one of several “parallel Earth” plots in TOS, contrived in part to save money, by avoiding “alien” sets, costumes, and makeup. Kirk and Spock get to wear flashy pin-stripe suits, hats, carry machine guns, and speak in gangster accents. Even the women wear guns on their garters (which you probably wouldn’t see in reality)! It’s esp. funny to see Spock try to fit the situation. Kirk makes up the rules of the card game “fizz bin” as he goes along. Shatner ad libbed the rules, so his pauses to think and the other actors’ confusion are genuine. The scene when Kirk puts his feet up on Krako’s table and declares that now the Federation is “taking over the whole ball of wax” is reminiscent of a scene in the gangster film Little Caesar (1931).
After filming wrapped, the studio received a letter from Caruso. “Oxmyx” thanked the crew of the Enterprise for creating the “syndicate” and noting that things were proceeding nicely on Sigma Iotia II. As he goes on in the letter, it is now the 1950s and he is sporting a crew-cut. He also mentioned wanting to visit Las Vegas which “seems like my kind of town.” LOL- what a creative guy!
 If you’re a fan of “The Godfather” and “Goodfellas,” then you’ll love this amusing episode… which plays like an eerily prescient parody of the original “Godfather.”
 There are great scenes as Kirk, and even more ridiculously, Spock try to mimic the dialect and nomenclature of the time. There is the priceless scene the two attempting to drive. Kirk jerks along, not quite getting the hang of the clutch, and Spock tells him he is a great captain, but a horrible, dangerous driver.
 I couldn’t stop laughing every time poor Scotty tries to decipher the gangster speak, with Kirk having to go from the mob language to Federation speech across the communicator to help him out.
-Excerpts from IMDB reviews