How Sharper Than a Serpent's Tooth

A probe leads the Enterprise to a huge serpent-shaped alien ship, which seizes it in an energy field. Its master introduces himself as Kukulkan, the god of Mayan and Aztec legend, and transports Kirk, McCoy, Scotty and Ensign Walking Bear, a Comanche helmsman, into a recreated ancient city that blends Aztec, Egyptian and Chinese styles. Kukulkan wants to know why humanity never finished the work he set it. Kirk realises the alien visited many early cultures, each of which kept only part of his teaching. By turning the city's serpent statues to reflect sunlight onto a device, the landing party summons Kukulkan in his true winged form, and they discover they are being kept like animals in a zoo. When Kirk insists humanity no longer needs a god to guide it, Kukulkan grows furious. Spock frees the Enterprise, which disables the alien ship, and Kirk persuades Kukulkan that people must grow up on their own. Kukulkan departs.