The Doctor and Susan, having just left the planet Tacunda, are travelling in the TARDIS. The Doctor has a crystal, called by the Tacunda people a "Blessing Star", which he fits into the console. He explains to Susan that the primitive Tacunda thought the crystal brought good luck, but in reality there is a microscopic empathic creature inside the crystal that responds to the desires of whoever is holding the crystal. Unfortunately for the Doctor, the crystal does not provide navigational help, but instead burns out the navigational system and deposits the TARDIS on 20th century Earth.