Following the signal of a mysterious probe, the Enterprise is immobilized by an alien whose ship resembles a winged serpent, and who claims to be Kukulkan the ancient god of the Mayan-Aztec people on Earth. Kukulkan transports Kirk, McCoy, Scotty, and Walking Bear to his ship, where they find an ancient city, and are told they must solve the puzzle of the city or the Enterprise will be destroyed.
