|Place of origin:||Earth|
|Main actor:||Karen Henson|
A fiery redhead in hair colour and temperament, Frost was a no-nonsense and efficient UNIT operative who had problems maintaining personal relationships.
Working undercover, Frost investigated Stranks, the owner of a night club suspected of selling a potent street drug called Mandrake. At the same time, the Seventh Doctor and Ace had been drawn to Earth by the alien energy structure known as the Mandragora Helix. It had contacted Stranks and used him to produce Mandrake, which sapped the will of its users and made them susceptible to the Helix's influence. The Doctor and Ace worked with Frost to thwart the Helix again. During the course of this venture, she received a field promotion to Colonel. (COMIC: The Mark of Mandragora)
Investigating the crash of a World War II fighter plane with the Seventh Doctor, Frost entered the mind of the dead pilot and discovered that the crash had been the result of a collision with a Q'Dhite ship which a local clerk, Alex Evening had turned into his own private, miniature world. The Doctor and Frost entered Evening's world with UNIT troops. They destroyed the illusion and sent Evening into an irreversible coma. (COMIC: Evening's Empire)
Behind the scenes
In TV: Aliens of London, one of the alien experts killed by the Slitheen in 10 Downing Street is a woman wearing the uniform of a US Army Major with the nametag "FROST". In early drafts of the script, the character was named as "Muriel Frost"; however, this dialogue did not make it to the screen, so it is unclear whether this character is Muriel Frost or not. (DWMSE 11)