Unicepter IV was a planet.
The Fourth Doctor took Sharon Davies with him to visit some of old friends of his on the planet. While there, he stopped the slinths from taking over after they had been feeding on the fear of the inhabitants' nightmares. (COMIC: Dreamers of Death)
The Fourth Doctor later tried to return to Unicepter IV to attend Sharon's wedding to Vernon Allen. (COMIC: Star Beast II)