A large diplomatic conference will take place on Babel, to discuss the contentious issue of whether to admit Corridan to the Federation. Delegates are divided, and some of their motives are less than pure. Among these delegates is Sarek of Vulcan - Spock's estranged father. Add a mysterious challenging spacecraft and a murderer aboard the Enterprise, and Kirk has his hands full. Then Kirk himself is stabbed, leaving him seriously injured at the very moment when Spock is due to donate blood so that McCoy can operate on Vulcan ambassador Sarek's damaged heart. The key to solving this puzzle will require deducing which of the many factions is willing to go to violent lengths to sabotage this conference.