- You may be looking for DI McMillan.
McMillen was a woman in the 42nd century who possessed a book with alien writing in it. It talked about the Galis Expedition. She found out that all they had to go on was local myths and that there was a black hole called K37 Gem 5 orbited by a planet. She sent Captain Walker and his crew to retrieve the energy source on Krop Tor to sustain "the Empire". (WC: Tardisode 8)
Behind the scenes
DWMSE 14 gives Ri Richards' role as "McMillen", several times in its overview, but "McMillan" in the cast list, presumably contrary to the shooting script.