On an idyllic planet the crew's memories and fantasies become real, with sometimes lethal results.
The Enterprise orbits a peaceful planet that seems perfect for rest. But as the crew beams down, they begin to meet figures from their memories and fantasies, including a white rabbit and a medieval knight, and some of them prove deadly to the visitors.
The episode is one of the lighter stories of the first season, with a famous reveal about who is behind the strange events. It is remembered for the gentle humour and a lively fight between Kirk and an old academy rival. It inspired a later animated sequel, Once Upon a Planet.