The Eye of the Beholder

The Enterprise investigates the disappearance of a science team near Lactra VII and finds their ship, the Ariel, abandoned in orbit. Kirk, Spock and McCoy beam down and are captured by the Lactrans, huge slug-like telepaths far more advanced than humans, who keep a zoo of creatures from many worlds. The landing party is placed in an enclosure with the Ariel's survivors: Lt Cdr Tom Markel, Randi Bryce and the seriously ill Lt Nancy Randolph. Learning that the Lactrans provide whatever their captives picture, the group concentrates until McCoy receives his medical kit. A similar attempt to get a communicator goes wrong when a young Lactran grabs it and is beamed aboard the Enterprise, where it reads Scotty's mind and absorbs the ship's library. The youngster returns with Scotty and convinces the adults that their captives are intelligent. The Lactrans free everyone, inviting them back in twenty or thirty centuries.