Chloris was a verdant planet, covered in dense, foggy forests.
History
A species of native, mobile plants called Wolfweeds were found on the planet, along with a group of primitive humanoids. These humanoids were ruled by courts, still used astrologers and fought with simple swords and daggers. Despite this, they did have an idea of space travel, though they couldn't go into space themselves.
The humanoids of Chloris were kept at a primitive level due to the scarcity of metals on the planet. This stopped any mass production of materials and also stopped any clear cutting of the forests. Whoever held the monopoly of metal held the power.
For many years, it was Lady Adrasta who held power. She saw her power threatened when the Tythonian ambassador, Erato, arrived and offered metal in exchange for chlorophyll. To solve her problem, Adrasta had him thrown into the pit. This pit led to the only mine on the planet, the one from which all metal came.
For fourteen years Erato stayed there, and Adrasta continued to rule. She threw people who displeased her into the pit where they were supposedly eaten by "the creature". Adrasta's people were unaware of Erato's true nature; they didn't even know what the creature looked like.
The Fourth Doctor, Romana and K9 arrived on Chloris and the Doctor jumped into the pit. Romana was taken prisoner by a gang of thieves. These bandits were common on Chloris and prized stolen metal most of all. Romana was freed by K9 and was in turn captured by Adrasta.
Adrasta believed that she no longer needed the creature to guard the mine as she now had the TARDIS. She led a party into the mines to kill the creature. There she encountered Erato who related his story of Adrasta's betrayal. Her people turned against her and Erato and the Wolfweeds killed her.
The Tythonians saw the imprisoning of their ambassador as an act of war and had sent a neutron star to destroy Chloris' sun. The resulting explosion would wipe out the system. The Doctor used his TARDIS' tractor beam to slow the star while Erato used his ship to halt its journey. Organon organised the trading agreement between Chloris and Tythonus that Erato had originally intended. (TV: The Creature from the Pit).
This was one of the planets that did not accept the format of star map produced by Kasterborous, preferring to make their own system. (PROSE: Short Trips: Zodiac).