 Spock has been behaving unprecedentedly erratic for a while. When McCoy finds it to be a growing medical risk, Kirk drags the truth out of him: it is the  blood fever , the one time in a Vulcan s life he regresses to a primitive, hormonal state of mind, setting out to mate for life. He is granted his first shore-leave in his entire career, to go to Vulcan, and requests Kirk and McCoy to join him for the equivalent of a marriage with his since age seven arranged fiancée, T Pring. But on Vulcan she interrupts the matrimony by calling the ancient challenge: a champion of her choice will fight Spock for her; even more surprising is her choice falls on Jim. Only when the first of two dueling weapons has been handed the humans understand the fight is to the death, too late to decline in front of T Pau, the presiding top official from Spocks family...