Superb Kirk episode has both Bones and Spock questioning his psychological state and duty to his command as he assumes the role of Ahab while a dangerous gaseous "vampire" cloud - which can alter it's form / molecular structure and attacks humanoid lifeforms, attracted to the iron in the blood - is the whale. When Kirk was an ensign on the Farragut, the cloud attacked and killed a number of his crew members, including his captain. What haunts him is that he froze momentarily, failing to fire his phaser. Not that it would have done any good, anyways. Good part for Stephen Brooks as the Farragut captain's son, now an officer on the Enterprise. He freezes just like Kirk did when an away team beams down to a planet the Federation is interested in for a particular strong mineral looking for the cloud, with one officer dead, another fatally drained, near death. Kirk battles his inner demons and faces an obsessive desire to kill the creature he considers intelligent, needing Spock to agree/confirm. Bones challenges him often in the episode, addressing whether or not his actions will delay shipment of medical supplies where they are needed elsewhere just to conquer a ghost from the past, annihilating the cloud at the cost of lives his quest jeopardizes. Spock's Vulcan blood, containing copper instead of iron, repulses the cloud and that just might be the answer. Antimatter once again is Kirk's go-to weapon, but he'll need to attract the cloud his way, with Brooks accompanying him to a planet for one final showdown. Seeing Kirk contending with a passionate need to vanquish a creature he considers evil, as his friends are concerned for his mental well- being lends itself to fireworks, and this gives Shather complexity to chew the fat on. Spock confronting the kid Kirk confines to quarters (for the slight mistake freezing) about not accepting failure, wallowing in the agony of it, is a good little scene as are Bones' confrontations with Kirk over the obsession. Dealing with the past, and closing that chapter on a high note, allows Kirk to put it behind him. And a young officer can be salvaged in the process, not having to live with his own shortcoming as long as Kirk did. Kirk snapping off at his crew, revealing a troubled soul needing a salve for his emotional wounds shows a vulnerability perfect for dramatic effect, his character tested and persevering. The cloud gives off a sickly sweet honey smell that tips off its presence, and the attraction to hemoglobin gives Kirk some advantage in bait.
Review of Obsession
