Cordelia Crozier

 was a scientist who was working on a project for an antidote for a disease. She wanted a Time Lord to practise on. Sil wanted to know the progress of her project. She used Anzor's TARDIS to lure the Sixth Doctor to London. She wanted to find the Time Lords' immunities to many diseases, and used both the Doctor and Anzor to find them. She was the daughter of Crozier, and blamed the Doctor for his death. Sil was her Guardian. She discovered that the Doctor's immunity is transmissible. (AUDIO: Antidote to Oblivion)