"The Immunity Syndrome"

The Enterprise is on her way to investigate the mysterious loss of contact with solar system Gamma 7A when Spock is the victim of a powerful psychic assault. He reports that he has just sensed the death of the all-Vulcan crew of the U.S. S. Intrepid. The Enterprise next encounters a "zone of darkness" which they quickly learn is a massive, amoeba-like single-celled organism. The creature is carving a path of destruction through the entire universe, and Kirk and Spock quickly realize that Gamma 7A and the crew of the Intrepid were among its victims. Kirk realizes that the Enterprise is the only hope of defeating the creature before it can end all life in the universe by reproducing. Spock suggests that someone pilot a shuttlecraft into the heart of the creature to determine its weaknesses, and both he and McCoy want to man the mission, but Kirk reluctanctly chooses Spock because of his Vulcan endurance. McCoy's description of all life in the universe taking the role of antibodies inside of the creature inspires Kirk to send the Enterprise into the creature as an antibody, where Kirk orders the detonation of an antimatter charge. The charge kills the creature just before it is able to reproduce, and the Enterprise finds Spock's shuttlecraft and proceeds on her way.

Story

While "The Immunity Syndrome" is a classic episode of Trek, it is really what is known as a "bottle show," an episode intended to save money by taking place completely onboard the Enterprise. The plot is not wholly original, seemingly tapping previous Star Trek episodes. The Enterprise had to stop the vampire cloud from reproducing and spreading death across the universe in "Obsession," and similar large-scale threats were faced in "The Doomsday Machine" and "The Changeling." What enables this story to avoid becoming a retread of past stories is the characterization, specifically, the elements of the story dealing with Spock and McCoy's friendship and Kirk's struggle in the face of seemingly impossible odds. Because of these classic Star Trek trademarks, "The Immunity Syndrome" takes its place as one of the classic episodes of the series.

Action

There's plenty of action in "The Immunity Syndrome," though it's all ship-based drama. The Enterprise must struggle to overcome to the draining power of the creature and goes through some rough riding in the process of finally destroying the creature.

Performances

The performances that make this episode belong to Shatner, Nimoy, and Kelley. Shatner yet again does a great job of playing a dauntless Kirk up against impossible odds, while Nimoy and Kelly both play their respective roles with the proper sense of playfulness and agitation. This is a crucial episode in the history of the Kirk/Spock/McCoy frienship.
Trektastic Moments

This is another episode that manages to be one long Trektastic Moment. The Enterprise faces a threat to all life in the universe and the odds are against their survival. Classic stuff. As mentioned previously, McCoy and Spock's banter and relationship here constitute Trektastic Moments, as well as the image of the giant space amoeba, a well-known and highly-regarded image in sci-fi history.

Overall

Despite a story similar to previous other Trek episodes, "The Immunity Syndrome" is a classic episode of Star Trek. Highest possible recommendation.

The episode's title card.

The Enterprise faces the giant space amoeba.

Spock and McCoy butt heads over who gets to rush to their death.