Ailla (Inferno Earth)

Ailla worked for the Celestial Intervention Agency in a parallel universe.

Ailla and Koschei had become stranded on Earth for several years when Koschei's TARDIS was irreparably damaged in a battle with a disembodied entity which used robotic bear-like creatures as its foot soldiers and also tried to shroud the world in a web-like substance. When the Conclave learned of the TARDIS's abilities to travel sideways in time from video surveillance records of the Third Doctor's arrival and his subsequent activities at the Inferno Project, this led to plans to escape their dead world. However, when Koschei refused to help the Conclave evacuate to a parallel Earth, he and Ailla were imprisoned and tortured for information about how to operate his TARDIS's control console, the only part of Koschei's ruined craft that was salvageable, which would be used by the Conclave to open dimensional portals to the regular Earth timeline.

Ailla eventually died at the hands of the Conclave and the Republican Security Forces, while Koschei was left in his final incarnation and kept alive, in agony, on life-support systems while the RSF tortured him, forcing him to regenerate until he'd exhausted his regeneration cycle. When he met his parallel self, Koschei asked after Ailla, with the Master said guardedly that she still lived and that he now travelled alone. (PROSE: The Face of the Enemy)