The TARDIS lands on an unnamed planet. On the scanner the travellers see rabbit-like robots. Vicki names them "Bunnoids". She and Steven head outside, but a Bunnoid enters the TARDIS and locks the door. Outside, Vicki and Steven are threatened by blue-skinned natives.
The Bunnoid in the TARDIS manipulates controls so that its Lapino master, a brain-creature, can communicate mentally with the Doctor. It tells him it feeds on emotion, and Vicki and Steven's fear will provide that emotion. However, they at first don't take the danger seriously, and the brain-creature is frustrated. It then receives a message from its homeworld, Lapino, saying that since it has neither returned nor contacted home, its ship will be destroyed. The brain-creature explains to the Doctor that it crashed on this planet some time ago. It needs emotions to either fix its ship or send a message back to Lapino. It decides to create real emotion in Steven and Vicki by killing one of them.
The Doctor convinces the brain-creature that there are other emotions that it can use, such as love. He and the brain-creature create a fictional scenario, based on the story Cinderella, for Steven and Vicki to play out. Unfortunately for the Doctor, the story requires three parts, and he is forced to play the role of fairy godmother.
The story concludes with Prince Steven and Princess Vicki falling in love. The brain-creature doesn't want to keep up the illusion, and says it isn't fair that the Doctor manipulated them, as he does with all his companions. The brain-creature uses the Doctor's guilt, and it is enough to send the message to Lapino.
The TARDIS crew take off, with Vicki and Steven retaining almost no memories of living out the story.
- Vicki is reading The Big Girls' Book of Bedtime Tales.
- The Doctor uses his glasses to read.
- The Lapino's ship is called Explorer.
to be added