Operation -- Annihilate!

The Enterprise is going to investigate what appears to be a very slow-moving viral form of mass-hysteria which has, over centuries, brought several thriving civilizations on many different planets down. Spock reviews the epidemiology of the phenomenon at the beginning of the episode, revealing that the trajectory of the epidemic places a Federation colony directly in its path. Sam Kirk, his wife and their son, live in this colony.

Captain Kirk is directly affected by his family's involvement in all of this, and Shatner does a very nice job of portraying a captain whose professionalism and rational judgment are threatened, and whose usual rational support structure (Spock) is also imperiled and unavailable. In a scene which was, unfortunately underexploited by the mediocre script, Dr. McCoy rises to the occasion and, surprisingly, fills both his usual role and that of the great first officer.

Herschel Daugherty directs this memorable episode of TOS, and does an admirable job with a somewhat weak script. The Stephen Carabatsos script creates some problems for the acting (particularly Nimoy, Barrett and Kelley), and - like his previous effort "Court Martial" - makes the pace a bit inconsistent. Kelley and Shatner are truly remarkable despite these challenges.

The episode also uses setting very nicely, with a very minimal use of backdrops and carefully chosen locations for rare open air shots. Additionally, Spock's character is very nicely examined, the developing rivalry and friendship between McCoy and Spock is enhanced, and the powerful - though unresolved - relationship between Christine Chapel and Spock begins. Finally, this (and the great earlier City on the Edge of Forever)is one of the first episodes to exploit the (unfortunately largely overlooked and unrecognized) subtlety of William Shatner's acting ability by placing Kirk's personal life in the way of his professional practice. This became a major theme as the series continued into its 2nd and 3rd seasons.

Parasitic flat fish will send you insane, once they've made it inside you're as good as slain, it's a fight to discover, a remedy to recover, from psychosis inducing such pain.

The population of the Deneva colony come under attack from a space borne parasite that subsequently kills all while putting its host under extreme physical and mental torture.

User commentator a_l_i_e_n from Canada does great job of summarizing plot of this episode.

Of interest to me is his comment "The futuristic architecture of the Denovan capital for example is a fine example of the show's use of outdoor locations. The art direction here is vivid, well constructed and definitely a cut above the usually unconvincing indoor sets they so often had to make due with."

In fact the location of this episode's set was the old TRW Defense and Space Systems Group campus in Redondo Beach, CA at Avaiation Blvd and Marine Ave (also adjacent, and just N. of old Redondo HS campus) where I used to work in the late 70s. It was called Space Park or Research Park (address was 1 Space Park, RB, CA) back then. The flight of concrete stairs they come down at beginning of episode was the path to the cafeteria/lecture presentation area. Rest of set (where creatures were stuck to walls and ceiling) was in a typical indoor waiting area in most any of the many architecturally stylish buildings on that campus.

This was always one of my favorite episodes as a kid: The Enterprise crew investigates an epidemic of "space madness" and traces the latest outbreak to a local human colony that just happens to be where Kirk's identical twin brother has been assigned as a research scientist. The fun really begins when it becomes apparent what the alien menace is, which are an invasion of flying interstellar space pancakes that make up a collective gestalt creature looking to spread it's way across the galaxy. It needs humanoids who can fly space ships to spread from colony to colony, and Kirk has to face the decision of his career when choosing between whether or not to just go back to the Sulaco and nuke them all from orbit. It's the only way to be sure ...

Just kidding. This was one of our favorite Star Trek adventures to act out when we were kids because you could use a bean bag as the pretend space pancake and smack each other on the back, beaming it with your wooden shop class phaser to save each other. The architecture in the city is also pretty rad, looks a lot like the State University at Albany campus I used to study at, which lo and behold was built at about the same time that the actual location (some sort of aerospace company's campus center) was made. It's a great episode for Spock and McCoy fans too, they have more to do than usual which may have been the result of Leonard Nimoy's surprise popularity with fans writing in -- much to the chagrin of William Shatner, who considered himself the focus of the show and resented any major actions that didn't center on Captain Kirk.

This one doesn't, and so it sort of sticks out. One of the best of the "overlooked episodes", and actually rather violent & filled with more physical suffering than usual for Star Trek.

If anyone doesn't see the similarities to RA Heinlein's Puppet Masters, well, I don't know what to say.