In ' (1991), McCoy and Kirk escape from a Klingon prison world, and the "Enterprise" crew stops a plot to prevent peace between the United Federation of Planets and the Klingon Empire. Kelley reprised the role for the "Encounter at Farpoint" pilot episode of ' (1987), insisting upon no more than the minimum Screen Actors Guild payment for his appearance. McCoy had attained the rank of admiral in the Trek timeline when this episode was aired, and he is stated to be 137 years of age. He would go on to become Chief of Starfleet Medical, with a special rank known as Branch Admiral. The fictional book "Comparative Alien Physiology" was written by McCoy, and was required reading at the Starfleet Medical Academy through the 2370s.