 Spock 's father , Sarek ( Mark Lenard ) , confronts Kirk about his son 's death . The pair learn that before he died , Spock transferred his katra , or living spirit , to McCoy . Spock 's katra and body are needed to lay him to rest on his homeworld , Vulcan , and without help , McCoy will die from carrying the katra . Disobeying orders , Kirk and his officers spring McCoy from detention , disable the USS Excelsior , and steal the Enterprise from Spacedock to return to the Genesis planet to retrieve Spock 's body . 
