Obsession offers a very extraordinary antagonist--a "monster" that's an intelligent gas, made of an element that's not supposed to exist "naturally", and that's able to transform itself as a means of camouflage. Although there are some very broad parallels to this idea in other episodes, including Who Mourns for Adonais?, the material is handled very uniquely here.
We are also presented with an intriguing and unusual exploration of Captain Kirk's psychology, and through that, a bit of Starfleet history. Kirk is the source of the title, Obsession. He harbors deeply buried guilt, stemming from an incident on another ship when he was still a junior officer. His guilt suddenly rises to the surface after encountering this episode's antagonist. Because of this, he becomes obsessed with conquering the "monster", and it affects his judgments seriously enough that his command of the Enterprise is threatened.
As good as it was, the original Star Trek didn't often get close to more gut-level, scary horror material. This episode does, largely because the antagonist is unpredictable, shape shifting and nearly invisible much of the time. It functions as more of a generalized token of a threat to one's life force, made more literal in the way that the "monster" attacks its victims and sustains itself. At times, Obsession's structure and content--including emotional content, almost resemble later horror sci-fi like Alien (1979), which could have easily been influenced by it.
This episode is also notable for some extended, unusual cooperation and agreement between Spock and McCoy.
We are also presented with an intriguing and unusual exploration of Captain Kirk's psychology, and through that, a bit of Starfleet history. Kirk is the source of the title, Obsession. He harbors deeply buried guilt, stemming from an incident on another ship when he was still a junior officer. His guilt suddenly rises to the surface after encountering this episode's antagonist. Because of this, he becomes obsessed with conquering the "monster", and it affects his judgments seriously enough that his command of the Enterprise is threatened.
As good as it was, the original Star Trek didn't often get close to more gut-level, scary horror material. This episode does, largely because the antagonist is unpredictable, shape shifting and nearly invisible much of the time. It functions as more of a generalized token of a threat to one's life force, made more literal in the way that the "monster" attacks its victims and sustains itself. At times, Obsession's structure and content--including emotional content, almost resemble later horror sci-fi like Alien (1979), which could have easily been influenced by it.
This episode is also notable for some extended, unusual cooperation and agreement between Spock and McCoy.