Synopsis:

When Spock starts acting emotional and erratic Kirk orders him to sickbay for a complete physical.  McCoy finds a deadly chemical imbalance is starting to build.  Spock is in the first stages of the Vulcan mating cycle, the Pon Farr.    If he does not return to Vulcan he will die.

Initially I rated this episode quite low.  As I considered it more though I have given it a higher rating for a couple of reasons.   First it has some good fighting scenes.  It also gives us a lot more data on the Vulcans and how their society is built.   Finally it has a number of plot twists and one extremely good looking lady playing Spock's intended.   Not only is she good looking but, as it turns out, deviously dangerous.    This episode is definately a must see although the ringing bells could have been left out and I am left to wonder if Earth is the only world that came up with useful weapons instead of odd, badly balanced, and hard to handle weapons.