Petra Williams (Inferno Earth)

In a parallel universe, Dr. Petra Williams was the second-in-command of the Inferno Project at the the Eastchester Scientific Labour Camp.

Biography
Unlike her counterpart in the Doctor's universe, whose hair hung loose, the alternate Petra wore her hair drawn up in a bun.

Dr. Williams was loyal to her employers until the true danger was revealed, after which she assisted the Third Doctor to get back to his own world. Brigade Leader Alastair Lethbridge-Stewart put pressure on her to connect the camp's nuclear reactor to the TARDIS console, hoping to use it to escape. She was last seen hugging Greg Sutton, with whom she had formed a relationship, as the lava from the shaft poured onto the Earth's surface. (TV: Inferno)

It is unclear as to whether Dr. Williams was related to Williams, Marianne Kyle's aide and Chief Petty Officer on the HMS Redoubt, who helped with the Inferno Earth invasion. (PROSE: The Face of the Enemy)