A troop of an intergalactic gladiators arrives on the planet, where they will hold their annual competition. Meanwhile, Smith, Will and the Robot work busily to repair a weather station. John comes to check on their progress, and the group is soon interrupted by a pair of large men in wrestling costumes who start a brawl.
A third man appears and introduces himself as Myko. Myko commends John for fighting so well, and asks John to join his “Gamma Games,” an intergalactic contest that requires a representative from the planet Earth. John politely refuses.
In exchange for riches and passages back to Earth, Smith promises Myko that he will be able to convince John to change his mind. Myko agrees to the terms, but it turns out that Myko is deceitful and dangerous, but Smith has no idea.
Smith tries to humiliate and pressure John into entering the fight, but still John refuses. Meanwhile, Myko reports back to his superiors. It would seem that the Gamma Games are a ruse, a way for leaders of Myko's planet to judge the strength of their enemies. An Earth man is needed so they can decide whether or not to attack the Earth.
Smith continues to pester John to the point where John gets so angry he nearly strikes the doctor. Will is hurt and confused by his father's unwillingness to fight.
Realizing that John will never change his mind, Doctor Smith and Will go to Myko to tell him. There they are permitted to watch some of the contestants in training, which is a very impressive sight. When Myko learns that John will not be participating in the games, he insists that Smith enter instead. He promises that Smith can pick his opponent, and Smith chooses Geoo, a man half his height. Unfortunately for Smith, it turns out that Geoo is a crafty fellow and can make himself disappear.
Penny, Will and the Robot help Smith train. John is suspicious of Myko’s intentions and asks about the purpose of the games. Myko lies and claims they are only for entertainment. That night Myko contacts his superiors again, and John and Don eavesdrop on his transmission, learning the truth about Myko's intentions. When John informs Smith that Earth’s safety hangs in the balance, Smith is unconcerned, smug in the thought that he is going to win. John forbids Smith from entering and orders the Robot to guard him. The Robot does so by padlocking Dr. Smith in a cage, but Smith manages to trick the Robot and escape. He arrives at the Gamma Games and fights... but Geoo, with his superior talents, easily wins.
Myko announces that earth people are weak and that Earth will be invaded and subdued. Fortunately, John arrives and insists on fighting to prove Myko wrong. He triumphs over Geoo by using strategy, but Myko will still not stop the invasion plans. Only when John challenges Myko himself and defeats him in a game of nerve does the alien back down, and the Earth is saved.
- Peter Brocco appears in the Star Trek episode "Errand of Mercy" as an Organian. He also appears in the 1952 Republic Pictures serial Radar Men from the Moon as the alien Krog.
- Mike Kellin was an Obie award winner who had a long and respected career in theater including playing Oscar Madison in the original Broadway run of "The Odd Couple" after Walter Matthau and Jack Klugman played the part. Bill Mumy later played a crewman named Kellin (named after Mike Kellin) in an episode of Star Trek: Deep Space 9.
- Harry Monty was in remarkably good shape as Geoo - Monty was in his early 60s when he filmed this episod
- Gamma 6 was a planet in Sector 630, located close to the automated planet. (Forbidden World) It had an unstable magnetic field. (The Astral Traveler)
- The Gamma Games were held on Gamma 6 on a regular basis. (Deadly Games of Gamma 6)
- When Myko starts to kill one of his fighters for losing a game, Dr. Smith talks him out of it. This is very impressive coming from Dr. Smith.
- Will tells Myko, “You wouldn’t understand, Sir. You’re too intelligent.”
- When training for the games, Smith orders the Robot to massage his back. One would find it hard to believe those cold metal hook-hands could in any way be relaxing!
- Before the match, Myko introduces “Professor Zachary Smith” rather then “Doctor Zachary Smith”
- To prevent him from entering the Gamma games, Robot locks Smith into a very large cage. Where did it come from?!
- Though the Robinsons have forbidden Smith from entering the competition (and locked him up in a cage with a guard posted in front) they very kindly leave all his fighting gear laid out nearby. Er... just in case he escapes and still wants to play.
- Doctor Smith came up with a bundle of insults for the Robot in this episode. The include: Jabbering Judas, Traitorous Tin-Plated Fugitive from a Junkyard, Roly-Poly Rowdy, Mechanical Monolith, Ineffectual Ineptitude, Clumsy Clod, Despotic Dunce, Hulking Mass of Mechanical Ignorance.
- Another funny line was when Dr. Smith says, "I promise not to run away! Isn’t my word good enough for you?"