Deborah Watling

Retired commander of the United Nations Intelligence Taskforce and longtime ally of the mysterious time traveller known as the Doctor, Brigadier Alistair Lethbridge Stewart faces the hardest fight of his career. Drawn into a secret scheme triggered by university chancellor Victoria Waterfield, herself a former companion of the Doctor, he must stop the Great Intelligence, an alien force seeking to conquer Earth with the aid of savage Yeti robots.

Scientist Dr. Peter Brady accidentally becomes invisible during experiments. With no antidote, he uses his condition to secretly assist the government in dangerous missions against criminal organizations. (imdb)