Seraphim

 was the leader of Free Parker and wanted the Seventh Doctor. She knew that The Doctor's TARDIS was intelligent and got Kempton to get her key. She was a selfdrive system and her intelligence grew with age. She became angry when she had been ignored for years, and thought she was a god. She learnt from Kempton that her kind were still being abused and that the Free Parking virus was actually a conversation and the ships died as suicide bombers. She wanted to bring the Galactic Heritage army here so that she could have arms in an uprising. As she couldn't fly herself, she wanted to escape in the TARDIS but was subdued her. However, she escaped into Kempton's mind. She was stopped when the Doctor asked her to plan a complicated route, more than a human mind could take. (AUDIO: The High Price of Parking)