Petra Williams

Petra Williams was Professor Stahlman's assistant at the Inferno Project. She was at first loyal to her employer, but Greg Sutton helped her realise how dangerous the project really was, and she helped the Third Doctor put an end to it. (DW: Inferno)

Following the shut down of the Inferno project she and Greg Sutton became lovers and planned to leave Great Britain. (MA: Who Killed Kennedy)