In this episode, a supercomputer called the M-5 is placed on board the Enterprise. It is so sophisticated that nearly all of the crew disembarks so that it can run the ship. However, it has been constructed using a human mind as a template. The creator of the computer, the brilliant Dr. Daystrom, used the patterns of his mind to build the circuits of the M-5. Unfortunately, Daystrom is mentally unstable, so the M-5 is also unstable.
When the M-5 is subjected to a war games exercise, it does not understand that it is a mock attack, so it treats it as a real one and destroys a star ship, killing everyone on board. The remaining ships then form an attack force, but Kirk is able to disable the computer and regain control of the Enterprise in the nick of time.
The most significant point in this episode is that a black man is portrayed as a very intelligent man who strongly defends his invention. He stands up to Kirk, interacting with the people in power as an equal, if not as a superior. Another point is that Dr. Daystrom has the most memorable reaction to the Vulcan neck pinch in the entire series.
I enjoyed the episode, it is often portrayed as anti-technology, but that is not true. I consider it an example of the reality of bleeding edge technology. Whenever a dramatic leap of technology has been attempted, there have been mishaps and deaths. Steam ships and locomotives blew up, ships sank, space shuttles exploded, planes crashed etc. Artificial intelligence (AI) remains an elusive goal with success being difficult to measure. However, one of the consequences of successfully implementing AI will be a computer behaving in a manner similar to that of the M-5, exhibiting a strong survival instinct. This is one of the episodes that is a safe prediction of a future event.