Adrasta gained power by holding the monopoly of the planet's metal. All of this metal came from the planet's only mine, the entrance to which was a pit that was guarded fiercely by Adrasta's men. She was aided by Karela and the Huntsman, the latter controlling Adrasta's Wolfweeds. These Wolfweeds had been grown in nurseries within the palace for her use.
Erato, an ambassador from Tythonus, which lacked chlorophyll but had an abundance of metal, came to Chloris to start trade negotiations. Adrasta had him thrown into the pit rather than lose her monopoly. Anyone who opposed or failed her was thrown into the pit to be eaten by Erato, now dubbed "the creature". She kept the origins of the creature a secret.
Fifteen years later, when the Fourth Doctor came to Chloris, Adrasta was interested in what he made of Erato's craft. She was interested in his theory that it was an egg. The Doctor threw himself into the pit and Adrasta took Romana II prisoner instead, hoping she knew something about the object. She also had K9 brought to her palace, as he was made of valuable metal.
From K9's data banks, Adrasta learned about the TARDIS. She saw its powers as a way to dominate the planet without the creature to protect her mine. She decided to have K9 kill the creature and took a party into the mine.
As they advanced on the creature, it created a protective barrier to block their approach. Adrasta had K9 attack it, but this proved fruitless. The Doctor broke through from the other side and she took him as a prisoner.
Erato approached the party while Adrasta was unprepared. She cowered in fear and tried to flee, but the Doctor held her. Suspecting her deceit, the Huntsman used the Wolfweeds to force Adrasta to use Erato's communicator. Erato told them, using Adrasta's own voice, how she had acted selfishly rather than for the good of her planet. In revenge, Erato then attacked her, as did the Wolfweeds. She was killed in seconds, and her body dissolved. (TV: The Creature from the Pit)