Dr Sophie Topolovic was part of the Fifth Galactic Surveyor Corps, a survey team of human pioneers exploring a ruined city on a planet orbiting a pulsar in 2724.
She became the team's commander after the previous commander Woodbridge was killed by the Quiet Ones, the planet's original inhabitants. She reluctantly worked together with the Second Doctor to try to stop, and later flee from, the Quiet Ones. The Doctor stayed behind to open the door to the surface for the rest of them to escape to, as the outside door could only be opened from the control room. The Doctor eventually left the base, and explained he had made contact with the Quiet Ones, and agreed to a truce in which Sophie's team could continue to safely learn about and communicate with the Quiet Ones, if they did it more quietly. While minutes had passed outside, for the Doctor it was a few years. (AUDIO: Shadow of Death)