dr. mccoy and mr. spock find themselves trap in a planet past ice age and while capt . kirk be in the same planet colonial period . however and it the former pair that have the most try time . besides the freezing temperature and sanctuary to be find only in cave and there be a third inhabitant and the beautiful and so sexy zarabeth ( mariette hartley ) . a spock spend more time in this era and he slowly begin to revert to the behavioral pattern of his ancestor and feel a natural attraction to zarabeth and throw caution to the wind about ever leave this place . only with dr. mccoy constant reminder do spock hold on to some grasp of reality . this stand a one of the few time when the character get to show some emotion and nimoy ( spock ) play it to the hilt and come close to knock the bejesus out of deforest kelly ( mccoy ) . surprise to previous installment and captain kirk ( william shatner ) wasn not allow to get the girl and another plus for this one . perennial old man ian wolfe assay the role of mr. atoz and the librarian responsible for send the trio into the past .