A blue planet with a blue sun located in the Acteon star sector. The Third Doctor first tried to take Jo Grant there soon after he was pardoned by the Time Lords (RRR, PPP). He eventually visited it alone, but found the planet full of hostile life forms. From that visit, he brought back a Blue Crystal which enabled him to cancel BOSS's hypnotic powers (TTT). Metebelis Three was later settled by a Lost Ship launched in the 22nd Century, which crashlanded there. Under the influence of its crystals, the Earth spiders which the ship carried mutated and ended up ruling the colonists. Approximately four hundred thirty years later, circa 2530 AD, the Spiders of Metebelis Three plotted to conquer Earth. They used Lupton's psychic circle to send one of their own to Earth to fetch the Blue Crystal required by the Great One. Their plans were thwarted by the Third Doctor, who eventually returned to give the Blue Crystal to the Great One. It killed her, and the Spiders, finally freeing the colonists (ZZZ).