This episode in itself justified the existence of the entire third season of Star Trek. Although one reviewer has ranked it (rather absurdly) as the 54th-best episode, it deserves a much higher rating.The relationship between Spock and McCoy takes center stage as they clash as well as work together on their "repsective tasks to complete before the Tholians complete theirs."An interesting story with action, suspense and some good dialog. Also unusual is the fact that this episode focuses on almost every character on board except Kirk. A refreshing change of pace.