Synopsis:

When a strange gaseous creature sucks all of the red blood cells out of three crewmen Kirk becomes obsessed with hunting it down.   His vendetta is revealed to be related to an experience that happened eleven years previous aboard the Farragut.   It is also revealed that one of his greatest sources of personal failure is tied up with this very same creature.   Now he must hunt it down and kill it before it procreates.

Another very good episode.   One thing I love about Star Trek is the bending phasers.  Notice the angle that phasers leave the ship and then the angley they travel through their target.   I know this has nothing to do with the episode but it is very well documented in this show.   This episode also does a good job of showing that guilt is not necessarily tied to reality.    Kirk's feelings of guilt and anger over his actions 11 years ago are not helped much by knowing that they wouldn't have made any difference.   It also doesn't change his vendetta against the creature.   This episode is pretty good and there is a lot more interpersonal conflict than normal which reveals the characters to us in a new and different manner.  But remember to watch out for those bending phasers.